[PATCH] t5404: relax overzealous test

In 0b294c0abf0 (make deleting a missing ref more quiet, 2008-07-08), we added a test to verify that deleting an already-deleted ref does not show an error.

Our test simply looks for the substring 'error' in the output of the `git push`, which might look innocuous on the face of it.

Suppose, however, that you are a big fan of whales. Or even better: your IT administrator has a whale of a time picking cute user names, e.g. referring to you (due to your like of India Pale Ales) as "one of the cuter rorquals" (see https://en.wikipedia.org/wiki/Rorqual to learn a thing or two about rorquals) and hence your home directory becomes /home/cuterrorqual. If you now run t5404, it fails! Why? Because the test calls `git push origin :b3` which outputs:

    To /home/cuterrorqual/git/t/trash directory.t5404-tracking-branches/.
     - [deleted]         b3

Note how there is no error displayed in that output? But of course "error" is a substring of "cuterrorqual". And so that `grep error output` finds something.

This bug was not, actually, caught having "error" as a substring of the user name but while working in a worktree called "colorize-push-errors", whose name was part of that output, too, suggesting that not even testing for the *word* `error` via `git grep -w error output` would fix the underlying issue.

This patch chooses instead to look for the prefix "error:" at the beginning of the line, so that there can be no ambiguity that any catch was indeed a message generated by Git's `error_builtin()` function.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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Published-As: https://github.com/dscho/git/releases/tag/fix-t5404-error-v1
Fetch-It-Via: git fetch https://github.com/dscho/git fix-t5404-error-v1
 t/t5404-tracking-branches.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)