Add test coverage for intern_atom and atom cache lifecycle

[Copilot]

• Understand intern_atom function and atom caching mechanism in xcb.py
• Add tests for predefined atoms (no XCB call) — mock xcb_intern_atom and assert_not_called
• Add tests for cache hits/misses — real connection, selective xcb_intern_atom mock
• Add tests for connect/disconnect updating _ATOM_CACHE — real connection, no mocking
• Add tests for only_if_exists parameter behavior — real X server
• Refactor into TestInternAtom class with shared autouse fixture using real xcb.connect()
• test_atom_cache_lifecycle uses real connections, no mocking at all
• Only LIB.xcb.xcb_intern_atom is mocked (not the whole LIB) where control/spying is needed
• Code review and security check passed

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[jholveck]

It's ok, but that's a lot of code. Can we compress and combine these some? Some of the repeated code could also go into methods on a test class. BTW, there's a running X server (typically Xvfb) in the usual test environment, so we can talk to it if needed, but we don't have to.

[Copilot]

It's ok, but that's a lot of code. Can we compress and combine these some? Some of the repeated code could also go into methods on a test class. BTW, there's a running X server (typically Xvfb) in ...

Refactored in 415fcde. The 9 standalone functions + helper are replaced by a TestInternAtom class with a shared setup_intern_atom autouse fixture that creates the connection, cache entry, mock, and LIB patch once per test. _set_atom_value() handles any per-test atom value changes. The connect/disconnect tests are merged into a single test_atom_cache_lifecycle function.

[jholveck]

Is there a point to mocking the connection? Can we just get the cache keys, create a new real connection, verify its address had been added to the cache keys, close the connection, and verify it was deleted?

[Copilot]

Done in 362c124. test_atom_cache_lifecycle now snapshots the existing cache keys, calls xcb.connect() to get a real connection, asserts the new key appeared with an empty dict, calls xcb.disconnect(), and asserts the key is gone and the cache is back to its original state.

[jholveck]

Most of our test code tests against a real X server; you can assume that a real X server (like Xvfb) is available in the CI/CD test environment. Is there anything that we're testing that requires a completely mocked connection? We might need to monkey-patch out xcb.LIB.xcb_intern_atom with a mock for test_cache_miss_calls_xcb_and_caches_result, if that can be done.

[Copilot]

Done in 362c124. The setup_intern_atom fixture now calls xcb.connect()/xcb.disconnect() for a real connection. Only LIB.xcb.xcb_intern_atom is selectively patched (via _mock_xcb_intern_atom) in the tests that need to spy on or control that call. test_only_if_exists_returns_none_when_missing and test_pointer_connection_uses_correct_cache_key talk directly to the real X server.