test(auth): cover every OAuth2 provider's construction

Instantiating each provider class exercises its __init__/super().__init__,
which codecov patch flags as uncovered when a new provider lands. Walking the
provider classes dynamically keeps every current and future provider covered
with no per-provider test edit.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: EricGustin

libs/tests/core/test_auth_providers.py

@@ -0,0 +1,54 @@
+"""Every OAuth2 provider class in ``arcade_core.auth`` must construct and carry its metadata.
+
+This walks the provider classes dynamically rather than naming them, so a newly added
+provider is covered the moment it lands -- no per-provider test edit. Each subclass's
+``__init__`` (its ``super().__init__`` call) only runs on instantiation, so constructing
+every provider here is also what exercises those lines under coverage.
+"""
+
+import inspect
+
+import pytest
+from arcade_core import auth as auth_module
+from arcade_core.auth import AuthProviderType, OAuth2
+
+
+def _provider_classes() -> list[type[OAuth2]]:
+    """Concrete OAuth2 provider classes defined in ``arcade_core.auth`` (OAuth2 itself excluded)."""
+    return [
+        obj
+        for _, obj in inspect.getmembers(auth_module, inspect.isclass)
+        if issubclass(obj, OAuth2)
+        and obj is not OAuth2
+        and obj.__module__ == auth_module.__name__
+    ]
+
+
+def test_provider_classes_are_discovered():
+    # Guards the parametrized tests below from silently collecting zero cases.
+    assert _provider_classes(), "no OAuth2 provider classes found in arcade_core.auth"
+
+
+@pytest.mark.parametrize("provider_cls", _provider_classes(), ids=lambda c: c.__name__)
+def test_provider_constructs_with_default_metadata(provider_cls: type[OAuth2]):
+    provider = provider_cls()
+    assert isinstance(provider.provider_id, str)
+    assert provider.provider_id
+    assert provider.provider_type == AuthProviderType.oauth2
+    assert provider.id is None
+    assert provider.scopes is None
+
+
+@pytest.mark.parametrize("provider_cls", _provider_classes(), ids=lambda c: c.__name__)
+def test_provider_accepts_id_and_scopes(provider_cls: type[OAuth2]):
+    provider = provider_cls(id="custom-provider-id", scopes=["scope.read", "scope.write"])
+    assert provider.id == "custom-provider-id"
+    assert provider.scopes == ["scope.read", "scope.write"]
+    # provider_id is the fixed well-known key and is not displaced by a custom id.
+    assert provider.provider_id == provider_cls().provider_id
+
+
+def test_provider_ids_are_unique():
+    # A copy-paste codegen slip that reused another provider's id would collide here.
+    ids = [cls().provider_id for cls in _provider_classes()]
+    assert len(ids) == len(set(ids)), f"duplicate provider_id values: {sorted(ids)}"