added error if meta not passed when config or actions are

testing/src/scenario/context.py

@@ -454,6 +454,10 @@ def test_foo():
     Use this when calling :meth:`run` to specify the event to emit.
     """
 
+    # def test_foo():
+    #     ctx = Context(MyCharm, config={"foo": "bar"})
+    #     ctx.run(..., State())
+
     def __init__(
         self,
         charm_type: type[CharmType],
@@ -503,13 +507,18 @@ def __init__(
                 spec: _CharmSpec[CharmType] = _CharmSpec.autoload(charm_type)
             except MetadataNotFoundError as e:
                 raise ContextSetupError(
-                    f"Cannot setup scenario with `charm_type`={charm_type}. "
-                    f"Did you forget to pass `meta` to this Context?",
+                    f"Cannot automatically setup scenario with `charm_type`={charm_type}. "
+                    "This is likely because this charm has some nonstandard repository setup and Scenario "
+                    "can't find the charmcraft|(metadata|config|actions) yamls in their usual location. "
+                    "Please parse and provide their contents manually via the `meta`, `config` "
+                    "and `actions` Context parameters.",
                 ) from e
 
         else:
             if not meta:
-                meta = {"name": str(charm_type.__name__)}
+                raise ContextSetupError(
+                    "Scenario doesn't support overriding `actions|config` without overriding `meta` too."
+                )
             spec = _CharmSpec(
                 charm_type=charm_type,
                 meta=meta,

testing/src/scenario/state.py

@@ -1622,7 +1622,8 @@ def _load_metadata(charm_root: pathlib.Path):
     def autoload(charm_type: type[CharmBase]) -> _CharmSpec[CharmType]:
         """Construct a ``_CharmSpec`` object by looking up the metadata from the charm's repo root.
 
-        Will attempt to load the metadata off the ``charmcraft.yaml`` file
+        Will attempt to load the metadata off the ``charmcraft.yaml`` file.
+        On failure, will fall back to the legacy ``metadata.yaml/actions.yaml/config.yaml`` files.
         """
         charm_source_path = pathlib.Path(inspect.getfile(charm_type))
         charm_root = charm_source_path.parent.parent

testing/tests/test_charm_spec_autoload.py

@@ -126,6 +126,23 @@ def test_no_meta_raises(tmp_path, legacy):
             Context(charm)
 
 
+@pytest.mark.parametrize("legacy", (True, False))
+@pytest.mark.parametrize(
+    "params",
+    (
+        {"actions": {"foo": "bar"}},
+        {"config": {"foo": "bar"}},
+    ),
+)
+def test_partial_meta_raises(tmp_path, legacy, params):
+    with create_tempcharm(
+        tmp_path, legacy=legacy, meta={"type": "charm", "name": "sergio"}
+    ) as charm:
+        # metadata not found:
+        with pytest.raises(ContextSetupError):
+            Context(charm, **params)
+
+
 @pytest.mark.parametrize("legacy", (True, False))
 def test_relations_ok(tmp_path, legacy):
     with create_tempcharm(