diff --git a/src/alire/alire-builds-hashes.adb b/src/alire/alire-builds-hashes.adb
index 16692c29f..012f0f588 100644
--- a/src/alire/alire-builds-hashes.adb
+++ b/src/alire/alire-builds-hashes.adb
@@ -104,6 +104,27 @@ package body Alire.Builds.Hashes is
                  Root.Configuration.Build_Profile (Rel.Name)'Image);
          end Add_Profile;
 
+         ------------------
+         -- Add_Switches --
+         ------------------
+
+         procedure Add_Switches is
+            --  List the exact switches used for compilation due to Alire, as
+            --  any changes in those will require regen of configuration files.
+            --  We add a single entry, alphabetically sorted.
+            Switches : AAA.Strings.Set;
+            Config   : Crate_Configuration.Global_Config :=
+                         Root.Configuration.all;
+         begin
+            for Switch of Config.Build_Switches (Root, Rel.Name)
+            loop
+               Switches.Include (Switch);
+            end loop;
+            Add ("switches",
+                 Rel.Name.As_String,
+                 Switches.To_Vector.Flatten (","));
+         end Add_Switches;
+
          -------------------
          -- Add_Externals --
          -------------------
@@ -214,6 +235,7 @@ package body Alire.Builds.Hashes is
 
          --  Add individual contributors to the hash input
          Add_Profile;       -- Build profile
+         Add_Switches;      -- Exact list of build switches
          Add_Configuration; -- Crate configuration variables
 
          --  These are only relevant for shared dependencies, as they don't
@@ -222,7 +244,17 @@ package body Alire.Builds.Hashes is
          if not Builds.Sandboxed_Dependencies then
             Add_Externals;     -- GPR externals
             Add_Environment;   -- Environment variables
-            Add_Compiler;      -- Compiler version
+
+            --  In the root crate we can skip compiler detection, as it has no
+            --  bearing on the hash or config regeneration. This allows most
+            --  operations in a crate without dependencies to succeed even in
+            --  absence of a configured compiler. Note that for linked crates,
+            --  even if they don't have a proper build dir, the hash is
+            --  important for dependents.
+            if not Root.Is_Root_Release (Rel.Name) then
+               Add_Compiler;   -- Compiler version
+            end if;
+
             Add_Dependencies;  -- Hash of dependencies
          end if;
 
diff --git a/src/alire/alire-builds.adb b/src/alire/alire-builds.adb
index 73ddf0f4d..f632b95f1 100644
--- a/src/alire/alire-builds.adb
+++ b/src/alire/alire-builds.adb
@@ -30,7 +30,11 @@ package body Alire.Builds is
    is
       Src    : constant Absolute_Path := Paths.Vault.Path
                                             / Release.Deployment_Folder;
-      Dst    : constant Absolute_Path := Builds.Path (Root, Release);
+      Dst    : constant Absolute_Path := Builds.Path (Root,
+                                                      Release,
+                                                      Subdir => False);
+      --  In case of monorepo, the first time the repo is deployed, it will be
+      --  synced in its entirety.
       Synced : Flags.Flag := Flags.Complete_Copy (Dst);
    begin
       Was_There := False;
@@ -87,11 +91,21 @@ package body Alire.Builds is
    ----------
 
    function Path (Root    : in out Roots.Root;
-                  Release : Releases.Release)
+                  Release : Releases.Release;
+                  Subdir  : Boolean)
                   return Absolute_Path
-   is (Builds.Path
-       / (Release.Deployment_Folder
-         & "_"
-         & Root.Build_Hash (Release.Name)));
+   is
+      Base : constant Absolute_Path :=
+               Builds.Path
+                 / (Release.Deployment_Folder
+                    & "_"
+                    & Root.Build_Hash (Release.Name));
+   begin
+      if Subdir and then Release.Origin.Is_Monorepo then
+         return Base / Release.Origin.Subdir;
+      else
+         return Base;
+      end if;
+   end Path;
 
 end Alire.Builds;
diff --git a/src/alire/alire-builds.ads b/src/alire/alire-builds.ads
index 0735f6167..c84316812 100644
--- a/src/alire/alire-builds.ads
+++ b/src/alire/alire-builds.ads
@@ -39,8 +39,11 @@ package Alire.Builds is
    --  Location of shared builds
 
    function Path (Root    : in out Roots.Root;
-                  Release : Releases.Release)
+                  Release : Releases.Release;
+                  Subdir  : Boolean)
                   return Absolute_Path;
-   --  Computes the complete path in which the release is going to be built
+   --  Computes the complete path in which the release is going to be built.
+   --  If Subdir and Release is in monorepo, include the extra path inside the
+   --  monorepo. Has no effect for ordinary releases.
 
 end Alire.Builds;
diff --git a/src/alire/alire-crate_configuration.adb b/src/alire/alire-crate_configuration.adb
index ebcf24bf5..e96776531 100644
--- a/src/alire/alire-crate_configuration.adb
+++ b/src/alire/alire-crate_configuration.adb
@@ -40,6 +40,11 @@ package body Alire.Crate_Configuration is
 
    subtype Crate_Name_Set is Containers.Crate_Name_Sets.Set;
 
+   procedure Make_Switches_Map (This     : in out Global_Config;
+                                Root     : in out Alire.Roots.Root;
+                                Rel_Vect : Crate_Name_Set);
+   --  Prepare the list of switches that apply to a release
+
    --  The Host info types below could be Enums instead of Strings. This would
    --  have the advantage of providing users the entire list of potential
    --  values. However, using enums in Ada would have a very high risk of
@@ -89,6 +94,23 @@ package body Alire.Crate_Configuration is
                            return Utils.Switches.Profile_Kind
    is (This.Profile_Map (Crate));
 
+   --------------------
+   -- Build_Switches --
+   --------------------
+
+   function Build_Switches (This  : in out Global_Config;
+                            Root  : in out Roots.Root;
+                            Crate : Crate_Name)
+                            return Utils.Switches.Switch_List
+   is
+   begin
+      --  Ensure they're up to date
+      Make_Switches_Map (This, Root,
+                         Containers.Crate_Name_Sets.To_Set (Crate));
+
+      return This.Switches_Map (Crate);
+   end Build_Switches;
+
    -----------------------
    -- Build_Profile_Key --
    -----------------------
diff --git a/src/alire/alire-crate_configuration.ads b/src/alire/alire-crate_configuration.ads
index 2bc654614..e05b48e8e 100644
--- a/src/alire/alire-crate_configuration.ads
+++ b/src/alire/alire-crate_configuration.ads
@@ -46,6 +46,14 @@ package Alire.Crate_Configuration is
                            return Utils.Switches.Profile_Kind
      with Pre => This.Is_Valid;
 
+   function Build_Switches (This  : in out Global_Config;
+                            Root  : in out Roots.Root;
+                            Crate : Crate_Name)
+                            return Utils.Switches.Switch_List
+     with Pre => This.Is_Valid;
+   --  The exact switches that apply to a crate (the ones that will be written
+   --  to their config .gpr files)
+
    function Is_Default_Profile (This  : Global_Config;
                                 Crate : Crate_Name)
                                 return Boolean;
diff --git a/src/alire/alire-properties-actions-executor.adb b/src/alire/alire-properties-actions-executor.adb
index e6b56035b..6fc40d9e8 100644
--- a/src/alire/alire-properties-actions-executor.adb
+++ b/src/alire/alire-properties-actions-executor.adb
@@ -143,7 +143,8 @@ package body Alire.Properties.Actions.Executor is
       end if;
 
       for Act of Release.On_Platform_Actions (Env, Now) loop
-         Trace.Detail ("Running action: " & Act.Image);
+         Trace.Detail ("Running action: " & Act.Image
+                       & " (cwd:" & Directories.Current & ")");
          Execute_Run (This       => Runners.Run (Act),
                       Capture    => Capture,
                       Err_To_Out => Err_To_Out,
diff --git a/src/alire/alire-roots.adb b/src/alire/alire-roots.adb
index 2184c42da..c7a9b2d7d 100644
--- a/src/alire/alire-roots.adb
+++ b/src/alire/alire-roots.adb
@@ -33,6 +33,41 @@ package body Alire.Roots is
 
    use type UString;
 
+   -------------------
+   -- Build_Prepare --
+   -------------------
+
+   procedure Build_Prepare (This           : in out Root;
+                            Saved_Profiles : Boolean;
+                            Force_Regen    : Boolean) is
+   begin
+      --  Check whether we should override configuration with the last one used
+      --  and stored on disk. Since the first time the one from disk will be be
+      --  empty, we may still have to generate files in the next step.
+
+      if Saved_Profiles then
+         This.Set_Build_Profiles (Crate_Configuration.Last_Build_Profiles);
+      end if;
+
+      This.Load_Configuration;
+      This.Configuration.Ensure_Complete;
+      --  For proceeding to build, the configuration must be complete
+
+      --  Ensure sources are up to date
+
+      if not Builds.Sandboxed_Dependencies then
+         This.Sync_Builds;
+         --  Changes in configuration may require new build dirs.
+      end if;
+
+      --  Ensure configurations are in place and up-to-date
+
+      This.Generate_Configuration (Full => Force or else Force_Regen);
+      --  Will regenerate on demand only those changed. For shared
+      --  dependencies, will also generate any missing configs not generated
+      --  during sync, such as for linked releases and the root release.
+   end Build_Prepare;
+
    -----------
    -- Build --
    -----------
@@ -182,31 +217,8 @@ package body Alire.Roots is
 
    begin
 
-      --  Check whether we should override configuration with the last one used
-      --  and stored on disk. Since the first time the one from disk will be be
-      --  empty, we may still have to generate files in the next step.
-
-      if Saved_Profiles then
-         This.Set_Build_Profiles (Crate_Configuration.Last_Build_Profiles);
-      end if;
-
-      This.Load_Configuration;
-      This.Configuration.Ensure_Complete;
-      --  For proceeding to build, the configuration must be complete
-
-      --  Ensure sources are up to date
-
-      if not Builds.Sandboxed_Dependencies then
-         This.Sync_Builds;
-         --  Changes in configuration may require new build dirs.
-      end if;
-
-      --  Ensure configurations are in place and up-to-date
-
-      This.Generate_Configuration (Full => Force);
-      --  Will regenerate on demand only those changed. For shared
-      --  dependencies, will also generate any missing configs not generated
-      --  during sync, such as for linked releases and the root release.
+      This.Build_Prepare (Saved_Profiles => Saved_Profiles,
+                          Force_Regen    => False);
 
       This.Export_Build_Environment;
 
@@ -766,11 +778,10 @@ package body Alire.Roots is
 
       This.Solution.Print_Hints (This.Environment);
 
-      --  Update/Create configuration files
-
-      if Builds.Sandboxed_Dependencies then
-         This.Generate_Configuration (Full => Force);
-      end if;
+      --  For sandboxed deps we could already generate config files, but for
+      --  shared builds we cannot yet until we are sure the configuration is
+      --  complete. To have the same behavior in both cases, we also delay
+      --  configuration generation to build time for sandboxed dependencies.
 
       --  Check that the solution does not contain suspicious dependencies,
       --  taking advantage that this procedure is called whenever a change
@@ -1431,7 +1442,7 @@ package body Alire.Roots is
                      return This.Release_Parent (Rel,
                                                  For_Deploy) / Rel.Base_Folder;
                   when For_Build =>
-                     return Builds.Path (This, Rel);
+                     return Builds.Path (This, Rel, Subdir => True);
                end case;
             end if;
          end;
@@ -1591,6 +1602,15 @@ package body Alire.Roots is
                              return Boolean
    is (Dep.Has_Release and then Dep.Crate = This.Release.Reference.Name);
 
+   ---------------------
+   -- Is_Root_Release --
+   ---------------------
+
+   function Is_Root_Release (This : in out Root;
+                             Name : Crate_Name)
+                             return Boolean
+   is (This.Release.Reference.Name = Name);
+
    ------------------------
    -- Sync_From_Manifest --
    ------------------------
@@ -1716,6 +1736,12 @@ package body Alire.Roots is
       begin
          This.Traverse (Removing_Post_Fetch_Flag'Access);
       end;
+
+      --  Regenerate config files to avoid the unintuitive behavior that after
+      --  an update they may still not exist (or use old switches).
+
+      This.Build_Prepare (Saved_Profiles => False,
+                          Force_Regen    => True);
    end Update;
 
    --------------------
@@ -1845,11 +1871,6 @@ package body Alire.Roots is
          This.Set (Solution => Needed);
          This.Deploy_Dependencies;
 
-         --  Update/Create configuration files
-         if Builds.Sandboxed_Dependencies then
-            This.Generate_Configuration (Full => True);
-         end if;
-
          Trace.Detail ("Update completed");
       end;
    end Update_Dependencies;
diff --git a/src/alire/alire-roots.ads b/src/alire/alire-roots.ads
index c55a5985e..57b3bc01c 100644
--- a/src/alire/alire-roots.ads
+++ b/src/alire/alire-roots.ads
@@ -179,6 +179,11 @@ package Alire.Roots is
                              return Boolean;
    --  Say if a state during Traverse is the Root release itself
 
+   function Is_Root_Release (This : in out Root;
+                             Name : Crate_Name)
+                             return Boolean;
+   --  Say if the root release matches the given name
+
    procedure Sync_From_Manifest (This     : in out Root;
                                  Silent   : Boolean;
                                  Interact : Boolean;
@@ -278,6 +283,15 @@ package Alire.Roots is
                         return String;
    --  Returns the build hash of a crate if the solution; computes on demand.
 
+   procedure Build_Prepare (This           : in out Root;
+                            Saved_Profiles : Boolean;
+                            Force_Regen    : Boolean);
+   --  Perform all preparations but the building step itself. This will require
+   --  complete configuration, and will leave all files on disk as if an actual
+   --  build were attempted. May optionally use saved profiles from the command
+   --  line (instead of manifests) and force full regeneration (for example,
+   --  during `alr update`)
+
    function Config_Outdated (This : in out Root;
                              Name : Crate_Name)
                              return Boolean;
diff --git a/src/alr/alr-commands-action.adb b/src/alr/alr-commands-action.adb
index 7755d920c..fb62cef0b 100644
--- a/src/alr/alr-commands-action.adb
+++ b/src/alr/alr-commands-action.adb
@@ -160,6 +160,10 @@ package body Alr.Commands.Action is
          Reportaise_Wrong_Arguments ("Invalid action: " & Arg);
       end if;
 
+      --  Ensure that all directories are ready
+      Cmd.Root.Build_Prepare (Saved_Profiles => False,
+                              Force_Regen    => False);
+
       Cmd.Root.Traverse (Doing => Run_One'Access);
       if not Some_Output then
          Put_Line ("No actions to run.");
diff --git a/testsuite/README.md b/testsuite/README.md
index 14c014001..5a212dbe0 100644
--- a/testsuite/README.md
+++ b/testsuite/README.md
@@ -34,3 +34,10 @@ $ pip install e3-testsuite
 # made it available with your PATH):
 $ ./run.py
 ```
+
+# Creating tests
+All tests are based on running a Python script. There are three test drivers:
+
+- `python-script`: run in host in both sandboxed and shared build mode.
+    - The build mode can be narrowed down with the `build_mode` attribute.
+- `docker-wrapper`: run in a pristine docker Ubuntu image in shared build mode.
diff --git a/testsuite/drivers/builds.py b/testsuite/drivers/builds.py
index d8479df71..9de84a282 100644
--- a/testsuite/drivers/builds.py
+++ b/testsuite/drivers/builds.py
@@ -16,6 +16,17 @@ def enable_shared() -> None:
     run_alr("config", "--global", "--set", "dependencies.shared", "true")
 
 
+def are_shared() -> bool:
+    """
+    Return True if shared builds are enabled
+    """
+    try:
+        return run_alr("config", "--global", "--get",
+                       "dependencies.shared").out.strip().lower() == "true"
+    except:
+        return False
+
+
 def clear_builds_dir() -> None:
     """
     Clear the shared build directory
@@ -56,6 +67,13 @@ def path() -> str:
     return alr_builds_dir()
 
 
+def vault_path() -> str:
+    """
+    Return the path to the read-only release vault.
+    """
+    return os.path.join(path(), "..", "releases")
+
+
 def sync() -> None:
     """
     Sync the shared build directory
diff --git a/testsuite/drivers/driver/python_script.py b/testsuite/drivers/driver/python_script.py
index 29fc90e57..4e86be460 100644
--- a/testsuite/drivers/driver/python_script.py
+++ b/testsuite/drivers/driver/python_script.py
@@ -1,7 +1,9 @@
+import copy
 import os
+import shutil
 import sys
 
-from drivers.alr import prepare_env, prepare_indexes
+from drivers.alr import prepare_env, prepare_indexes, run_alr
 from e3.testsuite.driver.classic import (ClassicTestDriver,
                                          TestAbortWithFailure,
                                          TestSkip)
@@ -14,7 +16,8 @@ class PythonScriptDriver(ClassicTestDriver):
     This test driver runs a Python script. For a testcase to succeeds, the
     script expects it to exit with status code 0, its standard error stream to
     be empty and its standard output stream to end with a line that contains
-    "SUCCESS". Anything else results in the test failing.
+    "SUCCESS". If a test must be skipped, it should print "SKIP: <reason>".
+    Anything else results in the test failing.
     """
 
     # This is a workaround for Windows, where attempting to use rlimit by e3-core
@@ -23,10 +26,11 @@ class PythonScriptDriver(ClassicTestDriver):
     def default_process_timeout(self):
         return None
 
-    def run(self):
+    def prepare(self) -> dict:
+        # prepare a private environment for Python scripts to run "alr".
+
         env = dict(os.environ)
 
-        # prepare a private environment for Python scripts to run "alr".
         config_dir = os.path.join(self.test_env['working_dir'],
                                   'alr-config')
         prepare_env(config_dir, env)
@@ -45,13 +49,19 @@ def run(self):
             path_for_drivers, os.path.pathsep, python_path
         ) if python_path else path_for_drivers
 
+        return env
+
+
+    def run_script(self, env):
         # Run the Python script with the current interpreter. check_call aborts
         # the test if the interpreter exits with non-zero status code.
-        p = self.shell([sys.executable, 'test.py'],
-                       env=env,
-                       cwd=self.test_env['working_dir'])
+        return self.shell([sys.executable, 'test.py'],
+                          env=env,
+                          cwd=self.test_env['working_dir'])
+
 
-        # Check that the last line in stdout is "SUCCESS" or "SKIP"
+    def check_result(self, p):
+        # Check that the test output is proper (no missing status)
         out_lines = p.out.splitlines()
         if out_lines and out_lines[-1] == 'SUCCESS':
             pass
@@ -60,3 +70,99 @@ def run(self):
         else:
             self.result.log += 'missing SUCCESS output line'
             raise TestAbortWithFailure('missing SUCCESS output line')
+
+
+    def save_working_dir(self):
+        # Save the working directory state for later restoration.
+
+        base = self.test_env['working_dir']
+        orig_name = ".orig"
+        orig = os.path.join(base, orig_name)
+
+        # Save the original files under ".orig" folder
+        os.mkdir(orig)
+        for f in os.listdir(base):
+            if f == orig_name:
+                continue
+            path = os.path.join(base, f)
+            if os.path.isfile(path):
+                shutil.copy(path, orig)
+            else:
+                shutil.copytree(path, os.path.join(orig, f))
+
+
+    def restore_working_dir(self):
+        # Restore the working directory to its initial state, by deleting
+        # everything and copying originals back from .orig dir
+
+        def make_writable(path):
+            # Make everything inside a directory writable recursively
+            for root, dirs, files in os.walk(path):
+                for d in dirs:
+                    os.chmod(os.path.join(root, d), 0o777)
+                for f in files:
+                    os.chmod(os.path.join(root, f), 0o666)
+
+        base = self.test_env['working_dir']
+        orig_name = ".orig"
+
+        # Delete anything not called ".orig"
+        for f in os.listdir(base):
+            if f != orig_name:
+                path = os.path.join(base, f)
+                if os.path.isfile(path):
+                    os.remove(path)
+                else:
+                    # Git marks some files read-only, so make them writable
+                    make_writable(path)
+                    shutil.rmtree(path)
+
+        # Restore the original files
+        orig = os.path.join(base, orig_name)
+        for f in os.listdir(orig):
+            path = os.path.join(orig, f)
+            if os.path.isfile(path):
+                shutil.copy(path, base)
+            else:
+                shutil.copytree(path, os.path.join(base, f))
+
+
+    def run(self):
+        # Run the test itself. Depending on the build mode, it may be run
+        # twice.
+        DEFAULT_MODE = "both"
+
+        pristine_env = self.prepare()
+
+        # Obtain the build mode for the test
+        mode = self.test_env.get('build_mode',
+                                 self.test_env.get('build-mode',
+                                                   DEFAULT_MODE))
+        # One of 'shared', 'sandboxed', or 'both'
+
+        # If mode is "both", track original files for later
+        if mode == "both":
+            self.save_working_dir()
+
+        # First run with shared builds disabled
+
+        if mode in ["sandboxed", "both"]:
+            self.result.log.log += "Build mode: SANDBOXED\n"
+            p = self.run_script(copy.deepcopy(pristine_env))
+            self.check_result(p)
+
+        # Second run with shared builds enabled
+
+        # Start by cleaning up anything the 1st run may have left behind
+        if mode == "both":
+            self.restore_working_dir()
+
+        if mode in ["shared", "both"]:
+            self.result.log.log += "Build mode: SHARED\n"
+            # Activate shared builds. Using "-c" is needed as the environment
+            # still isn't activated at the driver script level.
+            run_alr("-c", pristine_env["ALR_CONFIG"],
+                    "config", "--global", "--set",
+                    "dependencies.shared", "true")
+            p = self.run_script(copy.deepcopy(pristine_env))
+            self.check_result(p)
diff --git a/testsuite/fixtures/basic_index/gn/gnat_external/gnat_external-external.toml b/testsuite/fixtures/basic_index/gn/gnat_external/gnat_external-external.toml
new file mode 100644
index 000000000..f1171a6ba
--- /dev/null
+++ b/testsuite/fixtures/basic_index/gn/gnat_external/gnat_external-external.toml
@@ -0,0 +1,12 @@
+description = "GNAT is a compiler for the Ada programming language"
+name = "gnat_external"
+
+maintainers = ["alejandro@mosteo.com"]
+maintainers-logins = ["mosteo"]
+
+[[external]]
+kind = "version-output"
+# We look for make instead that should be always installed.
+version-command = ["make", "--version"]
+version-regexp = ".*Make ([\\d\\.]+).*"
+provides = "gnat"
diff --git a/testsuite/fixtures/basic_no_compiler_index/he/hello/hello-1.0.0.toml b/testsuite/fixtures/basic_no_compiler_index/he/hello/hello-1.0.0.toml
new file mode 100644
index 000000000..bf47cfcae
--- /dev/null
+++ b/testsuite/fixtures/basic_no_compiler_index/he/hello/hello-1.0.0.toml
@@ -0,0 +1,16 @@
+description = "\"Hello, world!\" demonstration project"
+long-description = "This is an example of long description in a multi-line string.\n\nMarkdown formating `can` be used to have \"nice\" display on the website.\n"
+name = "hello"
+version = "1.0.0"
+website = "example.com"
+authors = ["Bob", "Alice"]
+licenses = "GPL-3.0-only OR MIT"
+maintainers = ["alejandro@mosteo.com", "bob@example.com"]
+maintainers-logins = ["mylogin"]
+tags = ["tag1", "other-tag"]
+
+[[depends-on]]
+libhello = "^1.0"
+
+[origin]
+url = "file:../../../crates/hello_1.0.0"
diff --git a/testsuite/fixtures/basic_no_compiler_index/he/hello/hello-1.0.1.toml b/testsuite/fixtures/basic_no_compiler_index/he/hello/hello-1.0.1.toml
new file mode 100644
index 000000000..e67e218c6
--- /dev/null
+++ b/testsuite/fixtures/basic_no_compiler_index/he/hello/hello-1.0.1.toml
@@ -0,0 +1,29 @@
+description = "\"Hello, world!\" demonstration project"
+long-description = "This is an example of long description in a multi-line string.\n\nMarkdown formating `can` be used to have \"nice\" display on the website.\n"
+name = "hello"
+version = "1.0.1"
+website = "example.com"
+authors = ["Bob", "Alice"]
+licenses = "GPL-3.0-only OR MIT"
+maintainers = ["alejandro@mosteo.com", "bob@example.com"]
+maintainers-logins = ["mylogin"]
+tags = ["tag1", "other-tag"]
+
+[[depends-on]]
+libhello = "^1.0"
+
+[configuration.variables]
+Var1={type="Boolean"}
+Var2={type="String", default="str"}
+Var3={type="Enum", values=["A", "B"], default="A"}
+Var4={type="Integer", default=0}
+Var5={type="Integer", first=-1, last=1, default=0}
+Var7={type="Real", default=0.0}
+Var6={type="Real", first=-1.0, last=1.0, default=0.0}
+
+[configuration.values]
+hello.Var1=true # So far it is possible for a crate to set its own var
+libhello.Var1=false
+
+[origin]
+url = "file:../../../crates/hello_1.0.1"
diff --git a/testsuite/fixtures/basic_no_compiler_index/index.toml b/testsuite/fixtures/basic_no_compiler_index/index.toml
new file mode 100644
index 000000000..bad265e4f
--- /dev/null
+++ b/testsuite/fixtures/basic_no_compiler_index/index.toml
@@ -0,0 +1 @@
+version = "1.1"
diff --git a/testsuite/fixtures/basic_no_compiler_index/li/libhello/libhello-1.0.0.toml b/testsuite/fixtures/basic_no_compiler_index/li/libhello/libhello-1.0.0.toml
new file mode 100644
index 000000000..c46f09fab
--- /dev/null
+++ b/testsuite/fixtures/basic_no_compiler_index/li/libhello/libhello-1.0.0.toml
@@ -0,0 +1,23 @@
+description = "\"Hello, world!\" demonstration project support library"
+name = "libhello"
+version = "1.0.0"
+maintainers = ["alejandro@mosteo.com"]
+maintainers-logins = ["mylogin"]
+tags = ["libhello-tag1"]
+
+[configuration.variables]
+Var1={type="Boolean", default=true}
+
+[gpr-externals]
+TEST_GPR_EXTERNAL = ["gpr_ext_A", "gpr_ext_B", "gpr_ext_C"]
+TEST_FREEFORM_UNSET = "" # to test build hashing with an unset var
+
+[gpr-set-externals]
+TEST_GPR_EXTERNAL = "gpr_ext_B"
+TEST_UNDECLARED = "used_by_another_crate"
+
+[environment]
+TEST_ENV.set = "myenv"
+
+[origin]
+url = "file:../../../crates/libhello_1.0.0"
diff --git a/testsuite/fixtures/basic_no_compiler_index/ma/make/make-external.toml b/testsuite/fixtures/basic_no_compiler_index/ma/make/make-external.toml
new file mode 100644
index 000000000..eaf4b23eb
--- /dev/null
+++ b/testsuite/fixtures/basic_no_compiler_index/ma/make/make-external.toml
@@ -0,0 +1,8 @@
+description = "Utility for directing compilation"
+name = "make"
+maintainers = ["alejandro@mosteo.com"]
+maintainers-logins = ["mylogin"]
+
+[[external]]
+kind = "system"
+origin = [] # Empty on purpose to ensure unavailable in tests
diff --git a/testsuite/fixtures/compiler_only_index/gn/gnat_external/gnat_external-external.toml b/testsuite/fixtures/compiler_only_index/gn/gnat_external/gnat_external-external.toml
new file mode 100644
index 000000000..f1171a6ba
--- /dev/null
+++ b/testsuite/fixtures/compiler_only_index/gn/gnat_external/gnat_external-external.toml
@@ -0,0 +1,12 @@
+description = "GNAT is a compiler for the Ada programming language"
+name = "gnat_external"
+
+maintainers = ["alejandro@mosteo.com"]
+maintainers-logins = ["mosteo"]
+
+[[external]]
+kind = "version-output"
+# We look for make instead that should be always installed.
+version-command = ["make", "--version"]
+version-regexp = ".*Make ([\\d\\.]+).*"
+provides = "gnat"
diff --git a/testsuite/fixtures/compiler_only_index/index.toml b/testsuite/fixtures/compiler_only_index/index.toml
new file mode 100644
index 000000000..bad265e4f
--- /dev/null
+++ b/testsuite/fixtures/compiler_only_index/index.toml
@@ -0,0 +1 @@
+version = "1.1"
diff --git a/testsuite/fixtures/solver_index/gn/gnat_external/gnat_external-external.toml b/testsuite/fixtures/solver_index/gn/gnat_external/gnat_external-external.toml
new file mode 100644
index 000000000..f1171a6ba
--- /dev/null
+++ b/testsuite/fixtures/solver_index/gn/gnat_external/gnat_external-external.toml
@@ -0,0 +1,12 @@
+description = "GNAT is a compiler for the Ada programming language"
+name = "gnat_external"
+
+maintainers = ["alejandro@mosteo.com"]
+maintainers-logins = ["mosteo"]
+
+[[external]]
+kind = "version-output"
+# We look for make instead that should be always installed.
+version-command = ["make", "--version"]
+version-regexp = ".*Make ([\\d\\.]+).*"
+provides = "gnat"
diff --git a/testsuite/run.py b/testsuite/run.py
index 43843648e..8254dbbad 100755
--- a/testsuite/run.py
+++ b/testsuite/run.py
@@ -9,17 +9,15 @@
 
 from __future__ import absolute_import, print_function
 
-from argparse import ArgumentTypeError
-import sys
 import os.path
+import sys
+from argparse import ArgumentTypeError
 
 import e3.testsuite
 import e3.testsuite.driver
-from e3.testsuite.result import TestStatus
-
-from drivers.helpers import on_windows
-from drivers.driver.python_script import PythonScriptDriver
 from drivers.driver.docker_wrapper import DockerWrapperDriver
+from drivers.driver.python_script import PythonScriptDriver
+from drivers.helpers import on_windows
 
 
 class Testsuite(e3.testsuite.Testsuite):
diff --git a/testsuite/skels/global-index/test.yaml b/testsuite/skels/global-index/test.yaml
index 872fc1274..1a71b1b05 100644
--- a/testsuite/skels/global-index/test.yaml
+++ b/testsuite/skels/global-index/test.yaml
@@ -1,3 +1,5 @@
 driver: python-script
+build_mode: both  # one of shared, sandboxed, both (default)
 indexes:
-    basic_index: {}
+    basic_index:
+        in_fixtures: true
diff --git a/testsuite/skels/local-index/test.yaml b/testsuite/skels/local-index/test.yaml
index 0a859639c..a0ce9ba5e 100644
--- a/testsuite/skels/local-index/test.yaml
+++ b/testsuite/skels/local-index/test.yaml
@@ -1,4 +1,8 @@
 driver: python-script
+build_mode: both  # one of shared, sandboxed, both (default)
 indexes:
     my_index:
         in_fixtures: false
+# Note that shared builds require a detected compiler to be able to compute
+# build hashes, which is needed for many subcommands: build, get, printenv,
+# update... See compiler_only_index for an example of mock compiler detector.
diff --git a/testsuite/skels/no-index/test.yaml b/testsuite/skels/no-index/test.yaml
index 32c747b3f..45e528c23 100644
--- a/testsuite/skels/no-index/test.yaml
+++ b/testsuite/skels/no-index/test.yaml
@@ -1 +1,7 @@
 driver: python-script
+build_mode: both  # one of shared, sandboxed, both (default)
+indexes:
+    compiler_only_index: {}
+    # Note that shared builds require a detected compiler to be able to compute
+    # build hashes, which is needed for many subcommands: build, get, printenv,
+    # update...
\ No newline at end of file
diff --git a/testsuite/tests/action/trigger/test.yaml b/testsuite/tests/action/trigger/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/action/trigger/test.yaml
+++ b/testsuite/tests/action/trigger/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/alias/basic/test.yaml b/testsuite/tests/alias/basic/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/alias/basic/test.yaml
+++ b/testsuite/tests/alias/basic/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
diff --git a/testsuite/tests/build/hashes/compiler-input/test.py b/testsuite/tests/build/hashes/compiler-input/test.py
index 377bd9ae9..14a7f4c9a 100644
--- a/testsuite/tests/build/hashes/compiler-input/test.py
+++ b/testsuite/tests/build/hashes/compiler-input/test.py
@@ -23,9 +23,6 @@ def check_hash(signature: str) -> None:
 # Disable compiler selection, so the external is used
 run_alr("toolchain", "--disable-assistant")
 
-# Enable shared dependencies
-run_alr("config", "--set", "--global", "dependencies.shared", "true")
-
 # Init a crate without explicit compiler dependency
 init_local_crate("xxx")
 alr_with("crate_real")  # A regular crate in the index
diff --git a/testsuite/tests/build/hashes/compiler-input/test.yaml b/testsuite/tests/build/hashes/compiler-input/test.yaml
index 8185c03b5..80973aefa 100644
--- a/testsuite/tests/build/hashes/compiler-input/test.yaml
+++ b/testsuite/tests/build/hashes/compiler-input/test.yaml
@@ -1,4 +1,5 @@
 driver: python-script
+build_mode: shared
 indexes:
     toolchain_index:
         in_fixtures: true
diff --git a/testsuite/tests/build/hashes/compiler-missing/test.py b/testsuite/tests/build/hashes/compiler-missing/test.py
index 55e943291..13b372fe1 100644
--- a/testsuite/tests/build/hashes/compiler-missing/test.py
+++ b/testsuite/tests/build/hashes/compiler-missing/test.py
@@ -9,14 +9,18 @@
 # The index in this test has no compilers configured; hence we cannot locate
 # even the default external compiler.
 
-run_alr("config", "--set", "--global", "dependencies.shared", "true")
-
 # Init a crate without explicit compiler dependency
 # This does not fail because hashes are not computed until build time
 init_local_crate("xxx")
+
+# A standalone crate can be built because the compiler isn't used for the root
+# crate hash inputs
+run_alr("build")
+
+# Adding a dependency works because this doen't yet trigger an update/build
 run_alr("with", "libhello")
 
-# The build fails because we cannot compute the build hash without a compiler
+# The build fails because we cannot compute the dependency hash without a compiler
 p = run_alr("build", complain_on_error=False)
 assert_match(".*Unable to determine compiler version", p.out)
 
diff --git a/testsuite/tests/build/hashes/compiler-missing/test.yaml b/testsuite/tests/build/hashes/compiler-missing/test.yaml
index 8929d590a..42e4f842f 100644
--- a/testsuite/tests/build/hashes/compiler-missing/test.yaml
+++ b/testsuite/tests/build/hashes/compiler-missing/test.yaml
@@ -1,4 +1,4 @@
 driver: python-script
+build_mode: shared
 indexes:
-    basic_index:
-        in_fixtures: true
+    basic_no_compiler_index: {}
diff --git a/testsuite/tests/build/hashes/config-types/test.py b/testsuite/tests/build/hashes/config-types/test.py
index 2df2bb4ff..45a044dae 100644
--- a/testsuite/tests/build/hashes/config-types/test.py
+++ b/testsuite/tests/build/hashes/config-types/test.py
@@ -7,8 +7,6 @@
 from drivers.asserts import assert_eq
 from drivers import builds
 
-run_alr("config", "--set", "--global", "dependencies.shared", "true")
-
 init_local_crate()
 alr_with("hello=1.0.1")
 builds.sync()
@@ -27,6 +25,7 @@
     'external:HELLO_LIBRARY_TYPE=default\n'
     'external:LIBRARY_TYPE=default\n'
     'profile:hello=RELEASE\n'
+    'switches:hello=-O3,-fdata-sections,-ffunction-sections,-gnatW8,-gnatn\n'
     f'version:gnat_external={external_compiler_version()}\n',
     hash_input("hello"))
 
diff --git a/testsuite/tests/build/hashes/config-types/test.yaml b/testsuite/tests/build/hashes/config-types/test.yaml
index 8e25447d9..90efa1f5a 100644
--- a/testsuite/tests/build/hashes/config-types/test.yaml
+++ b/testsuite/tests/build/hashes/config-types/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
+build_mode: shared
 indexes:
     build_hash_index: {}
diff --git a/testsuite/tests/build/hashes/hashing-inputs/test.py b/testsuite/tests/build/hashes/hashing-inputs/test.py
index d56eb55fc..22006a6d7 100644
--- a/testsuite/tests/build/hashes/hashing-inputs/test.py
+++ b/testsuite/tests/build/hashes/hashing-inputs/test.py
@@ -11,7 +11,6 @@
 from drivers import builds
 from drivers.helpers import content_of
 
-run_alr("config", "--set", "--global", "dependencies.shared", "true")
 init_local_crate()
 alr_with("hello")
 
@@ -45,6 +44,11 @@
     'external:TEST_GPR_EXTERNAL=gpr_ext_B\n' # declared set GPR external
     'external:TEST_UNDECLARED=used_by_another_crate\n' # modified GPR external
     'profile:libhello=VALIDATION\n'          # build profile
+    'switches:libhello=-O3,-fdata-sections,-ffunction-sections,-g,-gnatVa,'
+    '-gnatW8,-gnata,-gnatn,-gnato,-gnatw.X,-gnatwa,-gnatwe,-gnaty-d,-gnaty3,'
+    '-gnatyA,-gnatyB,-gnatyI,-gnatyO,-gnatyS,-gnatya,-gnatyb,-gnatyc,-gnatye,'
+    '-gnatyf,-gnatyh,-gnatyi,-gnatyk,-gnatyl,-gnatym,-gnatyn,-gnatyp,-gnatyr,'
+    '-gnatyt,-gnatyu,-gnatyx\n'
     f'version:gnat_external={external_compiler_version()}\n',
                                              # compiler version
     hash_input("libhello"))
@@ -63,6 +67,11 @@
     'external:HELLO_LIBRARY_TYPE=default\n'
     'external:LIBRARY_TYPE=default\n'
     'profile:hello=VALIDATION\n'
+    'switches:hello=-O3,-fdata-sections,-ffunction-sections,-g,-gnatVa,'
+    '-gnatW8,-gnata,-gnatn,-gnato,-gnatw.X,-gnatwa,-gnatwe,-gnaty-d,-gnaty3,'
+    '-gnatyA,-gnatyB,-gnatyI,-gnatyO,-gnatyS,-gnatya,-gnatyb,-gnatyc,-gnatye,'
+    '-gnatyf,-gnatyh,-gnatyi,-gnatyk,-gnatyl,-gnatym,-gnatyn,-gnatyp,-gnatyr,'
+    '-gnatyt,-gnatyu,-gnatyx\n'
     f'version:gnat_external={external_compiler_version()}\n',
     hash_input("hello"))
 
@@ -74,7 +83,11 @@
     'external:LIBRARY_TYPE=default\n'
     'external:XXX_LIBRARY_TYPE=default\n'
     'profile:xxx=VALIDATION\n'
-    f'version:gnat_external={external_compiler_version()}\n',
+    'switches:xxx=-O3,-fdata-sections,-ffunction-sections,-g,-gnatVa,'
+    '-gnatW8,-gnata,-gnatn,-gnato,-gnatw.X,-gnatwa,-gnatwe,-gnaty-d,-gnaty3,'
+    '-gnatyA,-gnatyB,-gnatyI,-gnatyO,-gnatyS,-gnatya,-gnatyb,-gnatyc,-gnatye,'
+    '-gnatyf,-gnatyh,-gnatyi,-gnatyk,-gnatyl,-gnatym,-gnatyn,-gnatyp,-gnatyr,'
+    '-gnatyt,-gnatyu,-gnatyx\n',
     content_of(os.path.join("alire", "build_hash_inputs"))
 )
 
diff --git a/testsuite/tests/build/hashes/hashing-inputs/test.yaml b/testsuite/tests/build/hashes/hashing-inputs/test.yaml
index 8e25447d9..90efa1f5a 100644
--- a/testsuite/tests/build/hashes/hashing-inputs/test.yaml
+++ b/testsuite/tests/build/hashes/hashing-inputs/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
+build_mode: shared
 indexes:
     build_hash_index: {}
diff --git a/testsuite/tests/build/hashes/incomplete-config/test.py b/testsuite/tests/build/hashes/incomplete-config/test.py
index c649ea5a9..430de6684 100644
--- a/testsuite/tests/build/hashes/incomplete-config/test.py
+++ b/testsuite/tests/build/hashes/incomplete-config/test.py
@@ -3,13 +3,8 @@
 built/hashed
 """
 
-import shutil
-from drivers.alr import alr_with, external_compiler_version, init_local_crate, run_alr
-from drivers.builds import find_hash, hash_input
-from drivers.asserts import assert_eq, assert_match
-from drivers import builds
-
-run_alr("config", "--set", "--global", "dependencies.shared", "true")
+from drivers.alr import alr_with, init_local_crate, run_alr
+from drivers.builds import hash_input
 
 init_local_crate()
 alr_with("libhello=0.9")
diff --git a/testsuite/tests/build/hashes/incomplete-config/test.yaml b/testsuite/tests/build/hashes/incomplete-config/test.yaml
index 8e25447d9..90efa1f5a 100644
--- a/testsuite/tests/build/hashes/incomplete-config/test.yaml
+++ b/testsuite/tests/build/hashes/incomplete-config/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
+build_mode: shared
 indexes:
     build_hash_index: {}
diff --git a/testsuite/tests/build_profile/alr_build_switches/test.py b/testsuite/tests/build_profile/alr_build_switches/test.py
index b97b559c6..8b6ec7a29 100644
--- a/testsuite/tests/build_profile/alr_build_switches/test.py
+++ b/testsuite/tests/build_profile/alr_build_switches/test.py
@@ -71,13 +71,13 @@ def check_config_not_changed():
 check_config_changed()
 check_config(bin_config, 'release')
 
-# Alr with will re-generate the crate config and default to DEVELOPMENT
+# Alr with does not touch config, that happens at build time
 alr_with('lib_1', path='../lib_1')
-check_config_changed()
-check_config(bin_config, 'development')
+check_config_not_changed()
 
-# Build with default profile, the config should not change
+# Build with default profile, the config should change and revert to development
 run_alr('build')
-check_config_not_changed()
+check_config_changed()
+check_config(bin_config, 'development')
 
 print('SUCCESS')
diff --git a/testsuite/tests/build_profile/alr_build_switches/test.yaml b/testsuite/tests/build_profile/alr_build_switches/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/build_profile/alr_build_switches/test.yaml
+++ b/testsuite/tests/build_profile/alr_build_switches/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/build_profile/custom_profiles/test.yaml b/testsuite/tests/build_profile/custom_profiles/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/build_profile/custom_profiles/test.yaml
+++ b/testsuite/tests/build_profile/custom_profiles/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/build_profile/custom_switches/test.yaml b/testsuite/tests/build_profile/custom_switches/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/build_profile/custom_switches/test.yaml
+++ b/testsuite/tests/build_profile/custom_switches/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/build_profile/default/test.yaml b/testsuite/tests/build_profile/default/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/build_profile/default/test.yaml
+++ b/testsuite/tests/build_profile/default/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/build_profile/get-build-profile/test.yaml b/testsuite/tests/build_profile/get-build-profile/test.yaml
index 872fc1274..a1bd56a2e 100644
--- a/testsuite/tests/build_profile/get-build-profile/test.yaml
+++ b/testsuite/tests/build_profile/get-build-profile/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
\ No newline at end of file
diff --git a/testsuite/tests/build_profile/recursive/test.py b/testsuite/tests/build_profile/recursive/test.py
index f0c314d53..3f6448850 100644
--- a/testsuite/tests/build_profile/recursive/test.py
+++ b/testsuite/tests/build_profile/recursive/test.py
@@ -2,11 +2,14 @@
 Check build --profiles switch
 """
 
+from drivers import builds
 from drivers.alr import run_alr, init_local_crate, alr_pin, alr_manifest
 from drivers.helpers import lines_of, content_of
 
 import os
 
+from drivers.asserts import assert_contents, assert_match
+
 
 def check_profile(profile: str, file: str):
     line = f'   Build_Profile : Build_Profile_Kind := "{profile}";\n'
diff --git a/testsuite/tests/build_profile/recursive/test.yaml b/testsuite/tests/build_profile/recursive/test.yaml
index 32c747b3f..7654732d6 100644
--- a/testsuite/tests/build_profile/recursive/test.yaml
+++ b/testsuite/tests/build_profile/recursive/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
\ No newline at end of file
diff --git a/testsuite/tests/config/missing-config-default/test.py b/testsuite/tests/config/missing-config-default/test.py
index b334cd5d8..554bcf8a3 100644
--- a/testsuite/tests/config/missing-config-default/test.py
+++ b/testsuite/tests/config/missing-config-default/test.py
@@ -30,9 +30,12 @@
 assert_match('.*Configuration variables without a default remain unset\n',
              p.out)
 
-# Get without build must succeed with the missing values as warnings
+# Get without build succeeds as no config is needed yet
 p = run_alr("get", "hello=1.0.0", quiet=False)
 
+# Building must fail and complaint about missing variables
+os.chdir(glob("hello_1.0.0_*")[0])
+p = run_alr("build", complain_on_error=False, quiet=False)
 assert_match('.*Configuration variable \'hello.var1\' not set and has no default value.\n'
              '.*Configuration variable \'hello.var2\' not set and has no default value.\n'
              '.*Configuration variable \'hello.var3\' not set and has no default value.\n'
@@ -43,17 +46,7 @@
              '.*Configuration variable \'libhello.var3\' not set and has no default value.\n'
              '.*Configuration variable \'libhello.var4\' not set and has no default value.\n'
              '.*Configuration variable \'libhello.var5\' not set and has no default value.\n'
-             '.*Skipping generation of incomplete configuration files for crate hello\n'
-             '.*Skipping generation of incomplete configuration files for crate libhello\n'
-             '\n'
-             'hello=1.0.0 successfully retrieved.',
-             p.out)
-
-# Attempting to build now should fail
-os.chdir(glob("hello_1.0.0_*")[0])
-p = run_alr("build", complain_on_error=False)
-assert p.status != 0, "Build should have failed"
-assert_match('.*Configuration variables without a default remain unset\n',
+             '.*Configuration variables without a default remain unset\n',
              p.out)
 
 # Verify that providing the values in the manifest allows the build to work
diff --git a/testsuite/tests/config/missing-config-default/test.yaml b/testsuite/tests/config/missing-config-default/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/config/missing-config-default/test.yaml
+++ b/testsuite/tests/config/missing-config-default/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/config/shared-deps/test.py b/testsuite/tests/config/shared-deps/test.py
index ed458638e..84291e547 100644
--- a/testsuite/tests/config/shared-deps/test.py
+++ b/testsuite/tests/config/shared-deps/test.py
@@ -19,9 +19,6 @@ def check_in(file : str, expected : str) -> bool:
 vault_dir = alr_vault_dir()
 build_dir = alr_builds_dir()
 
-# Enable shared builds
-run_alr("config", "--global", "--set", "dependencies.shared", "true")
-
 # Create a crate with a dependency
 init_local_crate()
 alr_with("hello")
diff --git a/testsuite/tests/config/shared-deps/test.yaml b/testsuite/tests/config/shared-deps/test.yaml
index 8e25447d9..90efa1f5a 100644
--- a/testsuite/tests/config/shared-deps/test.yaml
+++ b/testsuite/tests/config/shared-deps/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
+build_mode: shared
 indexes:
     build_hash_index: {}
diff --git a/testsuite/tests/crate_config/basic/test.yaml b/testsuite/tests/crate_config/basic/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/crate_config/basic/test.yaml
+++ b/testsuite/tests/crate_config/basic/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/crate_config/gen_control/test.yaml b/testsuite/tests/crate_config/gen_control/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/crate_config/gen_control/test.yaml
+++ b/testsuite/tests/crate_config/gen_control/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/crate_config/value_conflict/test.py b/testsuite/tests/crate_config/value_conflict/test.py
index 69ad4cc11..b54bcadff 100644
--- a/testsuite/tests/crate_config/value_conflict/test.py
+++ b/testsuite/tests/crate_config/value_conflict/test.py
@@ -9,7 +9,7 @@
 import os
 import platform
 
-p = run_alr('get', 'hello_world', complain_on_error=False)
+p = run_alr('get', '--build', 'hello_world', complain_on_error=False)
 assert p.status != 0, "alr should have errored"
 
 print(p.out)
diff --git a/testsuite/tests/dockerized/misc/default-cache/test.py b/testsuite/tests/dockerized/misc/default-cache/test.py
index b97356f0d..f8afc0222 100644
--- a/testsuite/tests/dockerized/misc/default-cache/test.py
+++ b/testsuite/tests/dockerized/misc/default-cache/test.py
@@ -5,6 +5,7 @@
 
 import os
 
+from drivers import builds
 from drivers.alr import alr_with, init_local_crate, run_alr
 from drivers.helpers import contents
 
@@ -26,7 +27,7 @@
 # First, prevent an attempt at downloading a real compiler
 run_alr("toolchain", "--disable-assistant")
 
-run_alr("config", "--global", "--set", "dependencies.shared", "true")
+builds.enable_shared()  # Enabled here as we are using the Docker driver
 alr_with("crate_real")  # This release will go in the cache
 
 # Read-only vault
@@ -43,7 +44,7 @@
 # We hardcode this hash so we detect unwilling changes to our hashing scheme.
 # Every time this hash changes we must know the reason (changes in the hashing
 # procedures)
-hash = "cc2adb8312e543d98d36736d6220023a47a4508f547109334ee36916280e73ac"
+hash = "0774083df8ff003084c32cabdec6090a58b41c6be317cec0475df5eacbca0d23"
 assert \
     os.path.isdir(f"{base}/builds/crate_real_1.0.0_filesystem_{hash}"), \
     f"Shared build not found at the expected location: f{contents(base)}"
diff --git a/testsuite/tests/exec/basic/test.py b/testsuite/tests/exec/basic/test.py
index 0e5e1db73..a0eca167f 100644
--- a/testsuite/tests/exec/basic/test.py
+++ b/testsuite/tests/exec/basic/test.py
@@ -27,9 +27,16 @@
             ' alire context:" ${GPR_PROJECT_PATH}',
             quiet=False) # -q will hide the output of the exec command
 
-assert_match('.* GPR_PROJECT_PATH from alire context.*'
-             'hello_[0-9\.]*_filesystem.*'
-             'libhello_[0-9\.]*_filesystem.*',
+# These may appear in both orders depending on the cache location
+try:
+    assert_match('.* GPR_PROJECT_PATH from alire context.*'
+                'hello_[0-9\.]*_filesystem.*'
+                'libhello_[0-9\.]*_filesystem.*',
+                p.out, flags=re.S)
+except:
+    assert_match('.* GPR_PROJECT_PATH from alire context.*'
+             'libhello_[0-9\.]*_filesystem.*'
+             'hello_[0-9\.]*_filesystem.*',
              p.out, flags=re.S)
 
 print('SUCCESS')
diff --git a/testsuite/tests/exec/with_project/test.yaml b/testsuite/tests/exec/with_project/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/exec/with_project/test.yaml
+++ b/testsuite/tests/exec/with_project/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
diff --git a/testsuite/tests/get/external-tool-dependency/test.py b/testsuite/tests/get/external-tool-dependency/test.py
index 8ac1efb32..6509127bf 100644
--- a/testsuite/tests/get/external-tool-dependency/test.py
+++ b/testsuite/tests/get/external-tool-dependency/test.py
@@ -4,6 +4,7 @@
 
 import re
 
+from drivers import builds
 from drivers.alr import run_alr
 from drivers.asserts import assert_eq
 from drivers.helpers import compare, contents
@@ -16,7 +17,7 @@
 
 dir_content = contents('main_1.0.0_filesystem/')
 
-# The directrory for the external dependencies 'make' contains a version number
+# The directory for the external dependencies 'make' contains a version number
 # that can be different depending on the platform or version of the
 # distribution. We search through the content to find that directory and use it
 # in the expected output.
@@ -25,28 +26,33 @@
     if re.match('^.*/alire/cache/dependencies/make_.*_external$', elt):
         make_dep_dir = elt
 
-# Check folder contents
-compare(dir_content,
-        ['main_1.0.0_filesystem/alire',
-         'main_1.0.0_filesystem/alire.toml',
-         'main_1.0.0_filesystem/alire/alire.lock',
-         'main_1.0.0_filesystem/alire/build_hash_inputs',
-         'main_1.0.0_filesystem/alire/cache',
+# These only appear if dependencies are sandboxed
+extra = ['main_1.0.0_filesystem/alire/cache',
          'main_1.0.0_filesystem/alire/cache/dependencies',
          make_dep_dir,
          make_dep_dir + "/alire",
          make_dep_dir + "/alire/flags",
-         make_dep_dir + "/alire/flags/complete_copy",
-         'main_1.0.0_filesystem/alire/config.toml',
-         'main_1.0.0_filesystem/alire/flags',
+         make_dep_dir + "/alire/flags/complete_copy"]
+
+# Check folder contents
+compare(dir_content,
+        ['main_1.0.0_filesystem/alire',
+         'main_1.0.0_filesystem/alire.toml',
+         'main_1.0.0_filesystem/alire/alire.lock'] +
+         (extra if not builds.are_shared() else []) +
+        ['main_1.0.0_filesystem/alire/flags',
          'main_1.0.0_filesystem/alire/flags/complete_copy',
-         'main_1.0.0_filesystem/config',
-         'main_1.0.0_filesystem/config/main_config.ads',
-         'main_1.0.0_filesystem/config/main_config.gpr',
-         'main_1.0.0_filesystem/config/main_config.h',
          'main_1.0.0_filesystem/noop.gpr',
          'main_1.0.0_filesystem/src',
          'main_1.0.0_filesystem/src/noop.adb'
          ])
 
+if builds.are_shared():
+    # External tools that have no sources don't have a shared build dir:
+    try:
+        assert builds.find_dir("make")  # This should raise
+        raise Exception("Should not have found make build dir")
+    except:
+        pass
+
 print('SUCCESS')
diff --git a/testsuite/tests/get/git-local/test.py b/testsuite/tests/get/git-local/test.py
index d4a441ab3..86fb1ab6a 100644
--- a/testsuite/tests/get/git-local/test.py
+++ b/testsuite/tests/get/git-local/test.py
@@ -16,8 +16,6 @@
          'libfoo_1.0.0_9ddda32b/alire',
          'libfoo_1.0.0_9ddda32b/alire.toml',
          'libfoo_1.0.0_9ddda32b/alire/alire.lock',
-         'libfoo_1.0.0_9ddda32b/alire/build_hash_inputs',
-         'libfoo_1.0.0_9ddda32b/alire/config.toml',
          'libfoo_1.0.0_9ddda32b/alire/flags',
          'libfoo_1.0.0_9ddda32b/alire/flags/complete_copy',
          'libfoo_1.0.0_9ddda32b/b',
@@ -27,10 +25,6 @@
          'libfoo_1.0.0_9ddda32b/b/y/q',
          'libfoo_1.0.0_9ddda32b/b/z',
          'libfoo_1.0.0_9ddda32b/c',
-         'libfoo_1.0.0_9ddda32b/config',
-         'libfoo_1.0.0_9ddda32b/config/libfoo_config.ads',
-         'libfoo_1.0.0_9ddda32b/config/libfoo_config.gpr',
-         'libfoo_1.0.0_9ddda32b/config/libfoo_config.h'
          ])
 
 # Check as dependency
diff --git a/testsuite/tests/get/unpack-in-place/test.py b/testsuite/tests/get/unpack-in-place/test.py
index 18d72a6a3..afe1909bf 100644
--- a/testsuite/tests/get/unpack-in-place/test.py
+++ b/testsuite/tests/get/unpack-in-place/test.py
@@ -12,14 +12,8 @@
         ['libhello_1.0.0_filesystem/alire',
          'libhello_1.0.0_filesystem/alire.toml',
          'libhello_1.0.0_filesystem/alire/alire.lock',
-         'libhello_1.0.0_filesystem/alire/build_hash_inputs',
-         'libhello_1.0.0_filesystem/alire/config.toml',
          'libhello_1.0.0_filesystem/alire/flags',
          'libhello_1.0.0_filesystem/alire/flags/complete_copy',
-         'libhello_1.0.0_filesystem/config',
-         'libhello_1.0.0_filesystem/config/libhello_config.ads',
-         'libhello_1.0.0_filesystem/config/libhello_config.gpr',
-         'libhello_1.0.0_filesystem/config/libhello_config.h',
          'libhello_1.0.0_filesystem/libhello.gpr',
          'libhello_1.0.0_filesystem/src',
          'libhello_1.0.0_filesystem/src/libhello.adb',
diff --git a/testsuite/tests/index/bad-config-vars/test.py b/testsuite/tests/index/bad-config-vars/test.py
index 47bba445b..6ffa78423 100644
--- a/testsuite/tests/index/bad-config-vars/test.py
+++ b/testsuite/tests/index/bad-config-vars/test.py
@@ -42,9 +42,11 @@ def check_ok(var_def):
    p = run_alr('show', 'hello_world',
                complain_on_error=True, debug=False, quiet=True)
 
-
-os.remove(os.path.join("my_index", "index", "he", "hello_world",
-                       ".gitignore"))
+try:
+    os.remove(os.path.join("my_index", "index", "he", "hello_world",
+                        ".gitignore"))
+except:
+    pass  # Will have been removed by 1st test run
 
 check_error('var1=["plop"]', 'variable definition must be a table')
 check_error('var1={}', "configuration.variables.var1:")
diff --git a/testsuite/tests/install/dynamic-linking/test.yaml b/testsuite/tests/install/dynamic-linking/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/install/dynamic-linking/test.yaml
+++ b/testsuite/tests/install/dynamic-linking/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/install/executable-dependency/test.yaml b/testsuite/tests/install/executable-dependency/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/install/executable-dependency/test.yaml
+++ b/testsuite/tests/install/executable-dependency/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/install/static-linking/test.yaml b/testsuite/tests/install/static-linking/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/install/static-linking/test.yaml
+++ b/testsuite/tests/install/static-linking/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/misc/git-ungit/test.py b/testsuite/tests/misc/git-ungit/test.py
index 88ddb010d..4054d27cd 100644
--- a/testsuite/tests/misc/git-ungit/test.py
+++ b/testsuite/tests/misc/git-ungit/test.py
@@ -5,6 +5,7 @@
 import os
 import shutil
 
+from drivers import builds
 from drivers.alr import alr_with, crate_dirname, init_local_crate, run_alr
 from drivers.asserts import assert_file_exists
 
@@ -26,9 +27,13 @@
     init_local_crate()
     alr_with("libfoo")
 
-    assert_file_exists(os.path.join("alire", "cache", "dependencies",
-                                    foo_dir, ".git"),
-                       wanted=wanted)
+    if builds.are_shared():
+        assert_file_exists(os.path.join(builds.vault_path(), foo_dir, ".git"),
+                           wanted=False)
+    else:
+        assert_file_exists(os.path.join("alire", "cache", "dependencies",
+                                        foo_dir, ".git"),
+                        wanted=wanted)
 
     if not wanted:
         # Enable for next round
diff --git a/testsuite/tests/misc/sync-manual-edit/test.py b/testsuite/tests/misc/sync-manual-edit/test.py
index fe355f208..85179752b 100644
--- a/testsuite/tests/misc/sync-manual-edit/test.py
+++ b/testsuite/tests/misc/sync-manual-edit/test.py
@@ -5,6 +5,7 @@
 
 import os.path
 
+from drivers import builds
 from drivers.alr import run_alr, alr_touch_manifest
 from shutil import rmtree
 # from drivers.asserts import assert_eq, assert_match
@@ -31,7 +32,10 @@
     run_alr(cmd)
 
     # Check dependency folder is at the expected location:
-    assert os.path.isdir(target), "Directory missing at expected location"
+    if builds.are_shared():
+        assert builds.find_dir("libhello")
+    else:
+        assert os.path.isdir(target), "Directory missing at expected location"
 
     # Go back up and clean up for next command
     os.chdir("..")
diff --git a/testsuite/tests/misc/sync-manual-edit/test.yaml b/testsuite/tests/misc/sync-manual-edit/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/misc/sync-manual-edit/test.yaml
+++ b/testsuite/tests/misc/sync-manual-edit/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
diff --git a/testsuite/tests/misc/sync-missing-deps/test.py b/testsuite/tests/misc/sync-missing-deps/test.py
index ba91edda1..1ce92b910 100644
--- a/testsuite/tests/misc/sync-missing-deps/test.py
+++ b/testsuite/tests/misc/sync-missing-deps/test.py
@@ -7,6 +7,7 @@
 
 from drivers.alr import run_alr
 from drivers.builds import find_hash
+from drivers import builds
 
 # Create a new project and set up dependencies
 run_alr('init', '--bin', 'xxx')
@@ -24,7 +25,7 @@
 for round in range(2):
     if round == 2:
         # Prepare same test for shared dependencies
-        run_alr("config", "--set", "--global", "dependencies.shared", "true")
+        builds.enable_shared()
         run_alr("update")
         target = f"builds.path()/hello_1.0.1_filesystem_{find_hash('hello')}"
 
diff --git a/testsuite/tests/misc/sync-missing-deps/test.yaml b/testsuite/tests/misc/sync-missing-deps/test.yaml
index 872fc1274..5ccb3287e 100644
--- a/testsuite/tests/misc/sync-missing-deps/test.yaml
+++ b/testsuite/tests/misc/sync-missing-deps/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
+build_mode: sandboxed
 indexes:
     basic_index: {}
diff --git a/testsuite/tests/monorepo/basic/test.py b/testsuite/tests/monorepo/basic/test.py
index 16d4bf8a0..4d5137170 100644
--- a/testsuite/tests/monorepo/basic/test.py
+++ b/testsuite/tests/monorepo/basic/test.py
@@ -4,8 +4,8 @@
 """
 
 import os
-import shutil
 
+from drivers import builds
 from drivers.alr import run_alr, init_local_crate, alr_with, alr_publish
 from drivers.helpers import init_git_repo, on_windows
 # from drivers.asserts import assert_eq, assert_match
@@ -49,16 +49,18 @@
 init_local_crate("top")
 alr_with("mycrate")
 run_alr("build")
+base = (builds.find_dir("monoproject") if builds.are_shared()
+        else os.path.join("alire", "cache", "dependencies", f"monoproject_{commit[:8]}"))
 assert os.path.isfile(os.path.join(
-    "alire", "cache", "dependencies",
-    f"monoproject_{commit[:8]}", "mycrate", "bin",
+    base, "mycrate", "bin",
     f"mycrate{'.exe' if on_windows() else ''}")), \
     "Expected binary does not exist"
 
 # Also that the info file is there
-assert os.path.isfile(os.path.join(
-    "alire", "cache", "dependencies",
-    f"mycrate_0.1.0_in_monoproject_{commit[:8]}")), \
+deps_dir = (builds.vault_path() if builds.are_shared()
+            else os.path.dirname(base))
+infofile = f"mycrate_0.1.0_in_monoproject_{commit[:8]}"
+assert os.path.isfile(os.path.join(deps_dir, infofile)), \
     "Expected info file does not exist"
 
 print('SUCCESS')
diff --git a/testsuite/tests/monorepo/basic/test.yaml b/testsuite/tests/monorepo/basic/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/monorepo/basic/test.yaml
+++ b/testsuite/tests/monorepo/basic/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/monorepo/doubly-nested/test.py b/testsuite/tests/monorepo/doubly-nested/test.py
index 0c51634c9..6995e796a 100644
--- a/testsuite/tests/monorepo/doubly-nested/test.py
+++ b/testsuite/tests/monorepo/doubly-nested/test.py
@@ -3,8 +3,8 @@
 """
 
 import os
-import shutil
 
+from drivers import builds
 from drivers.alr import run_alr, init_local_crate, alr_with, alr_publish
 from drivers.helpers import init_git_repo
 from subprocess import run
@@ -46,9 +46,12 @@
 init_local_crate("top")
 alr_with("mychild")
 run_alr("build")
-assert os.path.isdir(os.path.join("alire", "cache", "dependencies",
-                                  f"monoproject_{commit[:8]}",
-                                  "myparent", "mychild")), \
+if builds.are_shared():
+    path = builds.find_dir("monoproject")
+else:
+    path = os.path.join("alire", "cache", "dependencies",
+                        f"monoproject_{commit[:8]}")
+assert os.path.isdir(os.path.join(path, "myparent", "mychild")), \
     "Expected directory does not exist"
 
 # Verify that "with"ing the parent does not result in a new checkout
diff --git a/testsuite/tests/monorepo/doubly-nested/test.yaml b/testsuite/tests/monorepo/doubly-nested/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/monorepo/doubly-nested/test.yaml
+++ b/testsuite/tests/monorepo/doubly-nested/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/monorepo/multi-commit/test.py b/testsuite/tests/monorepo/multi-commit/test.py
index 41a54621e..344948c85 100644
--- a/testsuite/tests/monorepo/multi-commit/test.py
+++ b/testsuite/tests/monorepo/multi-commit/test.py
@@ -5,13 +5,12 @@
 """
 
 import os
-import shutil
-
-from drivers.alr import run_alr, init_local_crate, alr_with, alr_publish
-from drivers.helpers import init_git_repo, on_windows, commit_all
-# from drivers.asserts import assert_eq, assert_match
 from subprocess import run
 
+from drivers import builds
+from drivers.alr import alr_publish, alr_with, init_local_crate, run_alr
+from drivers.helpers import commit_all, init_git_repo, on_windows
+
 # We create a repository with two nested crates that will act as the upstream
 # remote repository:
 start_dir = os.getcwd()
@@ -50,24 +49,36 @@
 alr_with("crate2")
 run_alr("build")
 
+
+def release_base(commit: str) -> str:
+    if builds.are_shared():
+        return builds.find_dir(f"monoproject_{commit[:8]}")
+    else:
+        return os.path.join("alire", "cache", "dependencies",
+                            f"monoproject_{commit[:8]}")
+
+
 assert os.path.isfile(os.path.join(
-    "alire", "cache", "dependencies",
-    f"monoproject_{commit1[:8]}", "crate1", "bin",
+    release_base(commit1), "crate1", "bin",
     f"crate1{'.exe' if on_windows() else ''}")), \
     "Expected binary does not exist"
 assert os.path.isfile(os.path.join(
-    "alire", "cache", "dependencies",
-    f"monoproject_{commit2[:8]}", "crate2", "bin",
+    release_base(commit2), "crate2", "bin",
     f"crate2{'.exe' if on_windows() else ''}")), \
     "Expected binary does not exist"
 
 # Also that the info files are there
+if builds.are_shared():
+    deps_dir = builds.vault_path()
+else:
+    deps_dir = os.path.join("alire", "cache", "dependencies")
+
 assert os.path.isfile(os.path.join(
-    "alire", "cache", "dependencies",
+    deps_dir,
     f"crate1_0.1.0_in_monoproject_{commit1[:8]}")), \
-    "Expected info file does not exist"
+    f"Expected info file does not exist"
 assert os.path.isfile(os.path.join(
-    "alire", "cache", "dependencies",
+    deps_dir,
     f"crate2_0.1.0_in_monoproject_{commit2[:8]}")), \
     "Expected info file does not exist"
 
diff --git a/testsuite/tests/monorepo/multi-commit/test.yaml b/testsuite/tests/monorepo/multi-commit/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/monorepo/multi-commit/test.yaml
+++ b/testsuite/tests/monorepo/multi-commit/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/pin/downgrade/test.py b/testsuite/tests/pin/downgrade/test.py
index 736779c78..5255dbee3 100644
--- a/testsuite/tests/pin/downgrade/test.py
+++ b/testsuite/tests/pin/downgrade/test.py
@@ -3,14 +3,13 @@
 """
 
 import os
+import re
 
-from drivers.alr import run_alr, alr_pin, alr_lockfile
-from drivers.asserts import assert_eq, assert_match
+from drivers import builds
+from drivers.alr import alr_lockfile, alr_pin, run_alr
+from drivers.asserts import assert_match
 from drivers.helpers import check_line_in
 
-import os
-import re
-
 
 # Verify that proper version of libchild is in the printed and disk solution
 def check_child(version, output, pinned):
@@ -26,8 +25,12 @@ def check_child(version, output, pinned):
     check_line_in(alr_lockfile(), f'version = "{version}"')
 
     # Verify dependency folders
-    assert os.path.exists('alire/cache/dependencies/libchild_' + version +
-                          '_filesystem')
+    if builds.are_shared():
+        run_alr('update')  # force hash computation
+        assert builds.find_dir('libchild_' + version + '_filesystem')
+    else:
+        assert os.path.exists('alire/cache/dependencies/libchild_' + version +
+                            '_filesystem')
 
 
 # Create a new "xxx" program project
diff --git a/testsuite/tests/pin/downgrade/test.yaml b/testsuite/tests/pin/downgrade/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/pin/downgrade/test.yaml
+++ b/testsuite/tests/pin/downgrade/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/pin/equivalent/test.py b/testsuite/tests/pin/equivalent/test.py
index b6695240d..0c74e2cf3 100644
--- a/testsuite/tests/pin/equivalent/test.py
+++ b/testsuite/tests/pin/equivalent/test.py
@@ -3,7 +3,7 @@
 """
 
 from drivers.alr import run_alr, alr_pin, init_local_crate
-from drivers.asserts import assert_eq, assert_match
+from drivers.asserts import assert_eq
 from drivers.helpers import init_git_repo, git_branch
 
 import os
diff --git a/testsuite/tests/pin/equivalent/test.yaml b/testsuite/tests/pin/equivalent/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/pin/equivalent/test.yaml
+++ b/testsuite/tests/pin/equivalent/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
diff --git a/testsuite/tests/pin/from-subdir/test.yaml b/testsuite/tests/pin/from-subdir/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/pin/from-subdir/test.yaml
+++ b/testsuite/tests/pin/from-subdir/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/pin/post-update/test.yaml b/testsuite/tests/pin/post-update/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/pin/post-update/test.yaml
+++ b/testsuite/tests/pin/post-update/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/pin/remote/test.yaml b/testsuite/tests/pin/remote/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/pin/remote/test.yaml
+++ b/testsuite/tests/pin/remote/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
diff --git a/testsuite/tests/pin/to-parent/test.yaml b/testsuite/tests/pin/to-parent/test.yaml
index 32c747b3f..fa855459b 100644
--- a/testsuite/tests/pin/to-parent/test.yaml
+++ b/testsuite/tests/pin/to-parent/test.yaml
@@ -1 +1,3 @@
 driver: python-script
+indexes:
+    compiler_only_index: {}
diff --git a/testsuite/tests/printenv/basic/test.py b/testsuite/tests/printenv/basic/test.py
index 2f4d711a7..10f91e8b8 100644
--- a/testsuite/tests/printenv/basic/test.py
+++ b/testsuite/tests/printenv/basic/test.py
@@ -5,6 +5,7 @@
 from glob import glob
 import os
 
+from drivers import builds
 from drivers.alr import run_alr
 from drivers.asserts import assert_eq, assert_match
 
@@ -27,10 +28,22 @@ def make_path(list):
     else:
         return "/".join(list)
 
+#  Force dependency syncing for the shared case
+run_alr("update")
+
 expected_hello_path = make_path(['.*', 'hello_1.0.1_filesystem'])
-expected_libhello_path = make_path(['.*', 'alire', 'cache', 'dependencies', 'libhello_1\.0\.0_filesystem'])
+expected_libhello_path = \
+make_path(['.*', os.path.basename(builds.find_dir('libhello'))]) \
+if builds.are_shared() else \
+make_path(['.*', 'alire', 'cache', 'dependencies', 'libhello_1\.0\.0_filesystem'])
 
-expected_gpr_path = os.pathsep.join([expected_hello_path, expected_libhello_path])
+#  Depending on the dependency location, both orders may occur
+expected_gpr_path = \
+    "(" \
+    f"{os.pathsep.join([expected_hello_path, expected_libhello_path])}" \
+    "|" \
+    f"{os.pathsep.join([expected_libhello_path, expected_hello_path])}" \
+    ")"
 
 assert_match('export ALIRE="True"\n'
              '.*'
diff --git a/testsuite/tests/printenv/env-during-fetch/test.py b/testsuite/tests/printenv/env-during-fetch/test.py
index 2ccf9daa0..5c57bfe0d 100644
--- a/testsuite/tests/printenv/env-during-fetch/test.py
+++ b/testsuite/tests/printenv/env-during-fetch/test.py
@@ -2,17 +2,22 @@
 Check that an env var is defined during dependency retrieval (get and with)
 """
 
-from glob import glob
 import os
 import re
+from glob import glob
 
+from drivers import builds
 from drivers.alr import run_alr
 from drivers.asserts import assert_match
 
 
-def verify_output(text):
-    assert_match('.*CHECKENV_TEST_VAR exists\n.*',
-                 text, flags=re.S)
+def verify_output(text, exists: bool):
+    if exists:
+        assert_match('.*CHECKENV_TEST_VAR exists\n.*',
+                    text, flags=re.S)
+    else:
+        assert "CHECKENV_TEST_VAR exists" not in text, \
+            "Unexpected output: " + text
 
 # The "checkenv" crate defines CHECKENV_TEST_VAR. Also, its executable prints
 # "CHECKENV_TEST_VAR exists" or "CHECKENV_TEST_VAR does NOT exist" when run.
@@ -24,14 +29,21 @@ def verify_output(text):
 # Build the crate to trigger the post-fetch action
 os.chdir(glob("checkparent*")[0])
 p = run_alr("build", complain_on_error=False)
-verify_output(p.out)
+verify_output(p.out, exists=True)
 
 # Create a crate from scratch and add the same dependency to perform the check
 # during retrieval by `with`
+
 run_alr("init", "--bin", "xxx")
 os.chdir("xxx")
 run_alr("with", "checkenv")
 p = run_alr("build")
-verify_output(p.out)
+# For shared builds, the crate has been already fetched as a dependency of
+# checkparent, so it should not emit anything. For sandboxed builds, it should
+# emit as expected.
+if builds.are_shared():
+    verify_output(p.out, exists=False)
+else:
+    verify_output(p.out, exists=True)
 
 print('SUCCESS')
diff --git a/testsuite/tests/printenv/env-during-fetch/test.yaml b/testsuite/tests/printenv/env-during-fetch/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/printenv/env-during-fetch/test.yaml
+++ b/testsuite/tests/printenv/env-during-fetch/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/printenv/linked-paths/test.yaml b/testsuite/tests/printenv/linked-paths/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/printenv/linked-paths/test.yaml
+++ b/testsuite/tests/printenv/linked-paths/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/publish/check-properties/test.yaml b/testsuite/tests/publish/check-properties/test.yaml
index 8929d590a..0415476b1 100644
--- a/testsuite/tests/publish/check-properties/test.yaml
+++ b/testsuite/tests/publish/check-properties/test.yaml
@@ -1,4 +1,5 @@
 driver: python-script
+build_mode: sandboxed
 indexes:
     basic_index:
         in_fixtures: true
diff --git a/testsuite/tests/publish/pin-removal/test.yaml b/testsuite/tests/publish/pin-removal/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/publish/pin-removal/test.yaml
+++ b/testsuite/tests/publish/pin-removal/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/publish/remote-origin-nonstd/test.py b/testsuite/tests/publish/remote-origin-nonstd/test.py
index f891f7e88..2651efc2d 100644
--- a/testsuite/tests/publish/remote-origin-nonstd/test.py
+++ b/testsuite/tests/publish/remote-origin-nonstd/test.py
@@ -59,4 +59,7 @@ def verify_manifest():
 p = run_alr("search", "--crates")
 assert "xxx" in p.out, "Crate not found in index contents"
 
+# Remove the index for the next test
+run_alr("index", "--del", "my_index")
+
 print('SUCCESS')
diff --git a/testsuite/tests/publish/remote-origin/test.py b/testsuite/tests/publish/remote-origin/test.py
index 0e87ece07..f35c29510 100644
--- a/testsuite/tests/publish/remote-origin/test.py
+++ b/testsuite/tests/publish/remote-origin/test.py
@@ -56,4 +56,7 @@ def verify_manifest():
 p = run_alr("search", "--crates")
 assert "xxx" in p.out, "Crate not found in index contents"
 
+# Remove the index for the next test
+run_alr("index", "--del", "my_index")
+
 print('SUCCESS')
diff --git a/testsuite/tests/solver/compiler-installed/test.py b/testsuite/tests/solver/compiler-installed/test.py
index 2b2e95373..e5c16fcab 100644
--- a/testsuite/tests/solver/compiler-installed/test.py
+++ b/testsuite/tests/solver/compiler-installed/test.py
@@ -3,11 +3,10 @@
 locally available one is used).
 """
 
-import subprocess
 import re
 
 from drivers.alr import run_alr, init_local_crate, alr_with
-from drivers.asserts import assert_eq, assert_match, match_solution
+from drivers.asserts import assert_match, match_solution
 
 # With no compiler selected, the external compiler in the environment should be
 # the only one available. We will verify this and capture its version (which is
diff --git a/testsuite/tests/update/selective/test.yaml b/testsuite/tests/update/selective/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/update/selective/test.yaml
+++ b/testsuite/tests/update/selective/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.py b/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.py
index 33a88b19b..bb2ea243e 100644
--- a/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.py
+++ b/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.py
@@ -20,6 +20,11 @@
 run_alr('with', 'libhello')
 run_alr('with', 'gpr_in_subdir')
 
+# In shared mode, a "with" won't generate config files yet (which is desirable
+# in case the withed crate has configuration variables without defaults). So we
+# need to trigger the generation of the config files.
+run_alr("update")
+
 check_line_in('config/myhello_config.gpr', 'with "libhello.gpr";')
 
 # When the crate declares a project file: `dir1/dir2/dir3/prj.gpr`, the with
diff --git a/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.yaml b/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.yaml
index 496a1d1a7..ea8ef3a20 100644
--- a/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.yaml
+++ b/testsuite/tests/with/auto-gpr-with/gpr_in_subdir/test.yaml
@@ -5,3 +5,5 @@ indexes:
     my_index:
         in_fixtures: false
         copy_crates_src: true
+    compiler_only_index:
+        in_fixtures: true
diff --git a/testsuite/tests/with/changes-info/test.yaml b/testsuite/tests/with/changes-info/test.yaml
index e0a82ba80..028a69369 100644
--- a/testsuite/tests/with/changes-info/test.yaml
+++ b/testsuite/tests/with/changes-info/test.yaml
@@ -1,4 +1,4 @@
 driver: python-script
 indexes:
-    solver_index:
-        in_fixtures: true
+    solver_index: {}
+    compiler_only_index: {}
\ No newline at end of file
diff --git a/testsuite/tests/with/equivalent/test.yaml b/testsuite/tests/with/equivalent/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/with/equivalent/test.yaml
+++ b/testsuite/tests/with/equivalent/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}
diff --git a/testsuite/tests/workflows/actions-as-dependency/test.py b/testsuite/tests/workflows/actions-as-dependency/test.py
index 8f56f5b20..69d1166f2 100644
--- a/testsuite/tests/workflows/actions-as-dependency/test.py
+++ b/testsuite/tests/workflows/actions-as-dependency/test.py
@@ -2,33 +2,34 @@
 Test pre-build/post-build/post-fetch executions in a crate that is a dependency
 """
 
-from drivers.alr import run_alr, init_local_crate, add_action, alr_with
-from drivers.asserts import assert_match
-from drivers.helpers import compare, contents, on_windows
+import os
 from glob import glob
 from pathlib import Path
 from shutil import rmtree
 
-import os
+from drivers import builds
+from drivers.alr import alr_with, init_local_crate, run_alr
+from drivers.asserts import assert_match
+from drivers.helpers import contents, neutral_path
 
 
-def check_expected(expected):
-    if not (expected in contents('.')):
+def check_expected(expected, path):
+    if not (expected in contents(path)):
         assert False, "%s expected in %s\n Got: %s" % \
-               (expected, '.', str(contents('.')))
+               (expected, path, str(contents(path)))
 
 
-def check_not_expected(expected):
-    if expected in contents('.'):
+def check_not_expected(expected, path):
+    if expected in contents(path):
         assert False, "%s is unexpected in %s\n Got: %s" % \
-               (expected, '.', str(contents('.')))
+               (expected, path, str(contents(path)))
 
 
-def check(file, to_be_or_not_to_be):
+def check(file, to_be_or_not_to_be, path):
     if to_be_or_not_to_be:
-        check_expected(file)
+        check_expected(file, path)
     else:
-        check_not_expected(file)
+        check_not_expected(file, path)
 
 
 def do_checks(path_to_dependency):
@@ -37,9 +38,9 @@ def do_checks(path_to_dependency):
     flag_post_build = path_to_dependency + "/test_post_build"
 
     # Immediately after adding the dependency, this is the situation:
-    check(flag_post_fetch, False)
-    check(flag_pre_build, False)
-    check(flag_post_build, False)
+    check(flag_post_fetch, False, path_to_dependency)
+    check(flag_pre_build, False, path_to_dependency)
+    check(flag_post_build, False, path_to_dependency)
 
     # Build with error, so only pre-build runs but not post-build
     Path(f"{path_to_dependency}/src/empty.adb").touch()
@@ -49,17 +50,17 @@ def do_checks(path_to_dependency):
     # Post build shouldn't be here because of build failure; post-fetch should
     # however now exist because a build has been attempted and post-fetch
     # succeeded (even if the build failed at a later stage)
-    check(flag_post_fetch, True)
-    check(flag_pre_build, True)
-    check(flag_post_build, False)
+    check(flag_post_fetch, True, path_to_dependency)
+    check(flag_pre_build, True, path_to_dependency)
+    check(flag_post_build, False, path_to_dependency)
 
     # Remove post-fetch to check it doesn't come back unexpectedly
     os.remove(flag_post_fetch)
 
     # Post build shouldn't be here because of build failure
-    check(flag_post_fetch, False)
-    check(flag_pre_build, True)
-    check(flag_post_build, False)
+    check(flag_post_fetch, False, path_to_dependency)
+    check(flag_pre_build, True, path_to_dependency)
+    check(flag_post_build, False, path_to_dependency)
 
     os.remove(flag_pre_build)
     os.remove(f"{path_to_dependency}/src/empty.adb")
@@ -68,23 +69,22 @@ def do_checks(path_to_dependency):
     run_alr('build')
 
     # pre/post-build expected for successful build
-    check(flag_post_fetch, False)
-    check(flag_pre_build, True)
-    check(flag_post_build, True)
+    check(flag_post_fetch, False, path_to_dependency)
+    check(flag_pre_build, True, path_to_dependency)
+    check(flag_post_build, True, path_to_dependency)
     return
 
-    # updating dependencies causes the post-fetch action to run:
-    run_alr('update')
-    check(flag_post_fetch, True)
-    check(flag_pre_build, True)
-    check(flag_post_build, True)
-
 
 # Initialize a crate and add as dependency the crate that contains the triggers
 init_local_crate("root", binary=False)  # Lib so all contents are compiled
 alr_with("hello_world")
+run_alr("update")
 # Test all triggers
-do_checks(glob("./alire/cache/dependencies/hello*")[0].replace('\\', '/'))
+if builds.are_shared():
+    base = neutral_path(builds.find_dir("hello_world"))
+else:
+    base = neutral_path(glob("./alire/cache/dependencies/hello*")[0])
+do_checks(base)
 
 # Repeat tests, for a crate that has been added as a linked dependency
 os.chdir("..")
diff --git a/testsuite/tests/workflows/actions-as-dependency/test.yaml b/testsuite/tests/workflows/actions-as-dependency/test.yaml
index 0a859639c..b3537ee9a 100644
--- a/testsuite/tests/workflows/actions-as-dependency/test.yaml
+++ b/testsuite/tests/workflows/actions-as-dependency/test.yaml
@@ -1,4 +1,6 @@
 driver: python-script
+build_mode: shared
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/workflows/actions-as-root/test.yaml b/testsuite/tests/workflows/actions-as-root/test.yaml
index 0a859639c..d6aa8a36d 100644
--- a/testsuite/tests/workflows/actions-as-root/test.yaml
+++ b/testsuite/tests/workflows/actions-as-root/test.yaml
@@ -2,3 +2,4 @@ driver: python-script
 indexes:
     my_index:
         in_fixtures: false
+    compiler_only_index: {}
diff --git a/testsuite/tests/workflows/get-build-run-clean/test.yaml b/testsuite/tests/workflows/get-build-run-clean/test.yaml
index 872fc1274..e2c5af220 100644
--- a/testsuite/tests/workflows/get-build-run-clean/test.yaml
+++ b/testsuite/tests/workflows/get-build-run-clean/test.yaml
@@ -1,3 +1,4 @@
 driver: python-script
 indexes:
     basic_index: {}
+    compiler_only_index: {}