fake-editor: add dumppath command

This allows us to assert the expected path in the test itself, rather
than in the fake editor.

cli/testing/fake-editor.rs

@@ -50,6 +50,12 @@ fn main() {
                 let dest_path = edit_script_path.parent().unwrap().join(dest);
                 fs::copy(&args.file, dest_path).unwrap();
             }
+            ["dumppath", dest] => {
+                let dest_path = edit_script_path.parent().unwrap().join(dest);
+                fs::write(&dest_path, args.file.to_str().unwrap()).unwrap_or_else(|_| {
+                    panic!("Failed to write file {}", args.file.to_str().unwrap())
+                });
+            }
             ["expect"] => {
                 let actual = String::from_utf8(fs::read(&args.file).unwrap()).unwrap();
                 if actual != payload {

cli/tests/test_config_command.rs

@@ -621,12 +621,13 @@ fn test_config_edit_user() {
     let repo_path = test_env.env_root().join("repo");
     let edit_script = test_env.set_up_fake_editor();
 
-    std::fs::write(
-        edit_script,
-        format!("expectpath\n{}", test_env.config_path().to_str().unwrap()),
-    )
-    .unwrap();
+    std::fs::write(edit_script, ["dumppath path"].join("\0")).unwrap();
     test_env.jj_cmd_ok(&repo_path, &["config", "edit", "--user"]);
+
+    assert_eq!(
+        std::fs::read_to_string(test_env.env_root().join("path")).unwrap(),
+        test_env.config_path().to_str().unwrap()
+    );
 }
 
 #[test]
@@ -636,15 +637,13 @@ fn test_config_edit_repo() {
     let repo_path = test_env.env_root().join("repo");
     let edit_script = test_env.set_up_fake_editor();
 
-    std::fs::write(
-        edit_script,
-        format!(
-            "expectpath\n{}",
-            repo_path.join(".jj/repo/config.toml").to_str().unwrap()
-        ),
-    )
-    .unwrap();
+    std::fs::write(edit_script, ["dumppath path"].join("\0")).unwrap();
     test_env.jj_cmd_ok(&repo_path, &["config", "edit", "--repo"]);
+
+    assert_eq!(
+        std::fs::read_to_string(test_env.env_root().join("path")).unwrap(),
+        repo_path.join(".jj/repo/config.toml").to_str().unwrap()
+    );
 }
 
 #[test]