fix: address review comments on version command PR

- Parametrize invalid combination tests (major/minor/patch/tag without project)
- Fix version scheme validation to use hasattr check instead of broken
  isinstance/issubclass on Protocol with non-method members
- Format test file with ruff

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: bearomorphism

commitizen/version_schemes.py

@@ -422,11 +422,16 @@ def get_version_scheme(settings: Settings, name: str | None = None) -> VersionSc
         raise VersionSchemeUnknown(f'Version scheme "{name}" unknown.')
     scheme = cast("VersionScheme", ep.load())
 
-    # `VersionProtocol` is a `@runtime_checkable` Protocol with properties, so
-    # `issubclass(scheme, VersionProtocol)` is not supported. The historical
-    # `isinstance(scheme, VersionProtocol)` check is only meaningful for instances;
-    # for loaded classes it is effectively a no-op for valid schemes.
-    if not isinstance(scheme, VersionProtocol):
+    # `VersionProtocol` is a `@runtime_checkable` Protocol, but `issubclass()` is not
+    # supported for Protocols with non-method members. We check an instance instead by
+    # verifying the loaded object is a class with the expected interface.
+    if isinstance(scheme, type):
+        # Check for a key method/attribute that VersionProtocol requires
+        if not hasattr(scheme, "bump"):
+            warnings.warn(
+                f"Version scheme {name} does not implement the VersionProtocol"
+            )
+    else:
         warnings.warn(f"Version scheme {name} does not implement the VersionProtocol")
 
     return scheme

tests/commands/test_version_command.py

@@ -147,19 +147,30 @@ def test_version_just_minor(config, capsys, version: str, expected_version: str)
     assert expected_version == captured.out
 
 
-@pytest.mark.parametrize("argument", ["major", "minor", "patch"])
-def test_version_just_major_error_no_project(config, capsys, argument: str):
-    commands.Version(
-        config,
-        {
-            argument: True,  # type: ignore[misc]
-        },
-    )()
+@pytest.mark.parametrize(
+    ("args", "expected_error"),
+    [
+        (
+            {"major": True},
+            "can only be used with MANUAL_VERSION, --project or --verbose.",
+        ),
+        (
+            {"minor": True},
+            "can only be used with MANUAL_VERSION, --project or --verbose.",
+        ),
+        (
+            {"patch": True},
+            "can only be used with MANUAL_VERSION, --project or --verbose.",
+        ),
+        ({"tag": True}, "Tag can only be used with --project or --verbose."),
+    ],
+)
+def test_version_invalid_combinations(config, capsys, args: dict, expected_error: str):
+    """Test that certain flag combinations produce errors."""
+    commands.Version(config, args)()  # type: ignore[arg-type]
     captured = capsys.readouterr()
     assert not captured.out
-    assert (
-        "can only be used with MANUAL_VERSION, --project or --verbose." in captured.err
-    )
+    assert expected_error in captured.err
 
 
 @pytest.mark.parametrize(
@@ -188,19 +199,6 @@ def test_version_with_tag_format(
     assert captured.out == expected_output
 
 
-def test_version_tag_without_project_error(config, capsys):
-    """Test --tag requires --project or --verbose"""
-    commands.Version(
-        config,
-        {
-            "tag": True,
-        },
-    )()
-    captured = capsys.readouterr()
-    assert not captured.out
-    assert "Tag can only be used with --project or --verbose." in captured.err
-
-
 @pytest.mark.parametrize(
     ("next_increment", "current_version", "expected_version"),
     [