Re: [PATCH 07/16] t5304: use test_path_is_* instead of "test -f"

Jeff King [off-list ref] writes:

This is slightly more robust (checking "! test -f" would not
notice a directory of the same name, though that is not
likely to happen here). It also makes debugging easier, as
the test script will output a message on failure.

Signed-off-by: Jeff King <redacted>
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This patch is totally optional. I did it while debugging t5304 (strange
how badly prune works when you accidentally invert the mtime check!)
and figured it might be worth keeping as a cleanup.

Looks sensible; thanks.