Add comprehensive test suite with GitHub Actions integration

[Copilot]

Implements a production-ready test suite for the canning timer application with CI/CD integration.

Changes

Test Coverage (16 tests)

• tests/test_main.py: Timer function execution and GUI window creation with mocking to avoid 15-minute waits
• tests/test_init.py: Package initialization and export validation
• tests/test_entrypoint.py: Entry point structure verification

CI Integration

• Updated .github/workflows/pytest.yml to install python3-tk system dependency for headless execution
• Added verbose output for CI debugging

Documentation

• docs/TESTING.md: Testing guide, coverage details, and local/CI execution instructions

Implementation Notes

Uses unittest.mock with threading to test 15-minute timers without blocking:

def _run_function_in_thread(self, func, timeout=2.0):
    """Helper method to run a function in a thread with timeout."""
    thread = threading.Thread(target=func)
    thread.daemon = True
    thread.start()
    thread.join(timeout=timeout)

@patch("time.sleep")
@patch("builtins.print")
def test_timeStart1_execution(self, mock_print, mock_sleep):
    """Test timeStart1 runs without errors when mocked."""
    self._run_function_in_thread(timeStart1)
    self.assertTrue(mock_print.called)
    self.assertTrue(mock_sleep.called)

No modifications to application code—tests are non-invasive.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• esm.ubuntu.com
  • Triggering command: /usr/lib/apt/methods/https (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

Write tests that can be implementd as GitHub Actions for this project.

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✨ Let Copilot coding agent set things up for you — coding agent works faster and does higher quality work when set up for your repo.

[github-actions]

Thank you for your contribution, please read and sign our CLA. Instructions on how to do so can be found in the CONTRIBUTING.md document.

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I have read the CLA Document, and I hereby sign the CLA.

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