tests: fix tests by clearing service_manager services (#5573)

* refactor(tests): add new fixtures to files tests

- Introduced new pytest fixtures for creating API keys, active users, and flows to streamline test setup.
- Updated file upload, download, list, and delete tests to utilize the new fixtures, improving clarity and maintainability.
- Ensured that flow IDs are correctly referenced in all file operations, enhancing test accuracy.
- Added cleanup logic in fixtures to maintain database integrity after tests.

This refactor improves the organization of test cases and ensures that they are more robust and easier to understand.

* fix(tests): clear services cache in test fixtures

- Added logic to clear the services cache in both `conftest.py` and `test_files.py` fixtures to ensure a clean state for tests.
- This change prevents potential interference between tests by resetting the service manager's factories and services before each test run.

* refactor(tests): streamline file upload tests and remove unused mocks

- Removed the mock implementation of StorageService from the test fixtures to simplify the test setup.
- Introduced new fixtures to set maximum file size upload limits, enhancing test flexibility.
- Updated file upload, download, and list tests to directly use the new fixtures, improving clarity and maintainability.
- Ensured that uploaded file content is accurately tested, reflecting changes in the upload and download logic.

src/backend/tests/conftest.py

@@ -354,7 +354,11 @@ async def client_fixture(
                 )
                 monkeypatch.setenv("LANGFLOW_LOAD_FLOWS_PATH", load_flows_dir)
                 monkeypatch.setenv("LANGFLOW_AUTO_LOGIN", "true")
+            # Clear the services cache
+            from langflow.services.manager import service_manager
 
+            service_manager.factories.clear()
+            service_manager.services.clear()  # Clear the services cache
             app = create_app()
             db_service = get_db_service()
             db_service.database_url = f"sqlite:///{db_path}"