# Investigation: C++ Unit Test Error Propagation

## Issue
The user reported that C++ unit tests, when run with `bash test --cpp --clean`, were not propagating errors up to `test.py`, often showing "0/1 runs" despite an underlying failure.

## Investigation Steps and Findings

1.  **Analyzed `test` script:** The `test` script (located at `C:\Users\niteris\dev\fastled10\test`) is a simple bash script that executes `uv run test.py "$@"`. This means all arguments, including `--cpp` and `--clean`, are passed directly to `test.py`.

2.  **Analyzed `test.py`:**
    *   `test.py` is the main test runner.
    *   It uses `ci.util.test_runner.runner` to orchestrate test execution.
    *   It includes a `try...except SystemExit` block in its `main` function to catch failures and set a `tests_passed` flag, ultimately exiting with a non-zero status code if `tests_passed` is `False`.

3.  **Analyzed `ci/util/test_runner.py`:**
    *   The `runner` function in this file determines test categories and, for C++ unit tests, delegates to `ci.util.meson_runner.run_meson_build_and_test`.
    *   It expects `run_meson_build_and_test` to return a `MesonTestResult` object, and if `result.success` is `False`, it calls `sys.exit(1)`.

4.  **Analyzed `ci/util/meson_runner.py`:**
    *   This file is responsible for building and running C++ unit tests using the Meson build system.
    *   The `run_meson_build_and_test` function orchestrates the process:
        *   It handles the `--clean` flag by removing the build directory, forcing a full rebuild.
        *   It calls `setup_meson_build` for Meson configuration.
        *   It calls `compile_meson` for compilation. This function uses `RunningProcess` to execute `meson compile` and checks its `returncode`. If compilation fails (non-zero `returncode`), it returns `False`.
        *   It calls `run_meson_test` for test execution. This function uses `RunningProcess` to execute `meson test`, parses its output to count passed/failed tests, and returns `MesonTestResult(success=False, ...)` if tests fail or `meson test` exits with a non-zero code.
    *   Crucially, if any of these sub-steps fail, `run_meson_build_and_test` returns a `MesonTestResult` with `success=False`.

5.  **Injected a Failing Test:** To confirm error propagation, a simple failing `TEST_CASE` (`CHECK(1 == 2);`) was temporarily added to `tests/doctest_main.cpp`.

6.  **Executed `bash test --cpp --clean` with Failing Test:**
    *   The command was executed, forcing a clean build and re-run of C++ tests.
    *   The output clearly showed:
        *   Meson setup and compilation proceeded successfully.
        *   The `doctest_main.cpp` file was compiled.
        *   The `[MESON] Streaming test execution complete:` section reported:
            *   `Tests run: 1`
            *   `Passed: 0`
            *   `Failed: 1`
        *   The overall summary indicated: `[MESON] ❌ Some tests failed (0/1 tests in X.XXs)`. 
        *   The `run_shell_command` tool reported `Exit Code: 1`.

## Conclusion

The investigation confirms that the error *is* propagating correctly from the C++ unit test (via doctest) through the Meson build system, `ci/util/meson_runner.py`, `ci/util/test_runner.py`, and finally to `test.py`, which then exits with a non-zero status code (1) to the shell.

The initial observation of "0/1 runs" was likely due to:
*   The specific C++ test not failing in a way that `meson test` could categorize as a "run" (e.g., a crash before test execution could begin).
*   The test being skipped due to fingerprint caching (which the `--clean` flag successfully bypasses).
*   A misinterpretation of partial output.

The current test infrastructure correctly identifies and propagates C++ unit test failures.

## Remediation
The temporary failing test case in `tests/doctest_main.cpp` has been removed.
