Simon McVittie e9c217adc1 test-basic: Don't fail if head -2 exits before flatpak does ...

The output might be written to the pipe by `flatpak --help` and/or read
from the pipe by `head -2` in more than one batch. If `head -2` reads
the first two lines before `flatpak --help` has written everything, it
will exit, causing the pipe to have no process at the read end. This
results in `flatpak --help` being killed by `SIGPIPE` next time it tries
to write to the pipe, because it has not opted out of this behaviour
(as shell tools usually shouldn't).

We're running under `set -o pipefail`, so this causes a nonzero exit
status that makes the test fail. Worse, this failure is intermittent,
because `head -2` *usually* doesn't exit until `flatpak --help` has
already written out everything it is going to write - it depends on
the precise behaviour of read(), write() and kernel scheduling.

We know that `flatpak --help` output is not *that* long, so it's OK
for `flatpak --help` not to be terminated early: we can send it all
into an intermediate file, and then run `head` on the file.

Signed-off-by: Simon McVittie <smcv@collabora.com>

2021-04-12 11:07:10 +02:00

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