Function test_capture_fd_logging_handler

tests/test_testing.py:600–642

capture='fd' captures logging output from a handler holding a stale stderr reference (issue #2827). stdlib logging.StreamHandler grabs sys.stderr at configuration time. Under normal CliRunner (sys-level capture), the handler still writes to the original stream object and output is l

(tmp_path)

@needs_fd_capture
def test_capture_fd_logging_handler(tmp_path):
    class="st">"""capture=&class="cm">#x27;fd' captures logging output from a handler holding a stale
    stderr reference (issue class="cm">#2827).

    stdlib logging.StreamHandler grabs sys.stderr at configuration time.
    Under normal CliRunner (sys-level capture), the handler still writes
    to the original stream object and output is lost. fd-level capture
    redirects the underlying file descriptor, so the writes are captured.
    class="st">"""
    import logging

    class="cm"># Create a writer backed by the real fd 2, simulating a handler
    class="cm"># configured at import time before pytest or CliRunner replaced
    class="cm"># sys.stderr. open(2, closefd=False) mirrors the real scenario:
    class="cm"># the original sys.stderr is a TextIOWrapper -> BufferedWriter ->
    class="cm"># FileIO(fd=2).
    stale_stderr = open(2, class="st">"w", closefd=False)  class="cm"># noqa: SIM115
    handler = logging.StreamHandler(stale_stderr)
    handler.setFormatter(logging.Formatter(class="st">"%(message)s"))

    logger = logging.getLogger(fclass="st">"click_test_{tmp_path.name}")
    logger.addHandler(handler)
    logger.setLevel(logging.INFO)
    logger.propagate = False

    @click.command()
    def cli():
        logger.info(class="st">"log from stale handler")
        click.echo(class="st">"normal echo")

    class="cm"># sys-level capture misses the log line (it bypasses sys.stderr).
    runner_sys = CliRunner(capture=class="st">"sys")
    result_sys = runner_sys.invoke(cli)
    assert class="st">"normal echo" in result_sys.output
    assert class="st">"log from stale handler" not in result_sys.output

    class="cm"># fd-level capture catches it by redirecting fd 2.
    runner_fd = CliRunner(capture=class="st">"fd")
    result_fd = runner_fd.invoke(cli)
    assert class="st">"normal echo" in result_fd.output
    assert class="st">"log from stale handler" in result_fd.output

    logger.removeHandler(handler)


@needs_fd_capture