test_ok2/changelog/7091.improvement.rst

When ``fd`` capturing is used, through ``--capture=fd`` or the ``capfd`` and
``capfdbinary`` fixtures, and the file descriptor (0, 1, 2) cannot be
duplicated, FD capturing is still performed. Previously, direct writes to the
file descriptors would fail or be lost in this case.
Perform FD capturing even if the FD is invalid The `FDCapture`/`FDCaptureBinary` classes, used by `capfd`/`capfdbinary` fixtures and the `--capture=fd` option (set by default), redirect FDs 1/2 (stdout/stderr) to a temporary file. To do this, they need to save the old file by duplicating the FD before redirecting it, to be restored once finished. Previously, if this duplicating (`os.dup()`) failed, most likely due to that FD being invalid, the FD redirection would silently not be done. The FD capturing also performs python-level redirection (monkeypatching `sys.stdout`/`sys.stderr`) which would still be done, but direct writes to the FDs would fail. This is not great. If pytest is run with `--capture=fd`, or a test is using `capfd`, it expects writes to the FD to work and be captured, regardless of external circumstances. So, instead of disabling FD capturing, keep the redirection to a temporary file, just don't restore it after closing, because there is nothing to restore to. 2020-03-16 05:32:59 +08:00			When ``fd`` capturing is used, through ``--capture=fd`` or the ``capfd`` and
			``capfdbinary`` fixtures, and the file descriptor (0, 1, 2) cannot be
			`duplicated, FD capturing is still performed. Previously, direct writes to the`
			`file descriptors would fail or be lost in this case.`