[PATCH v4 01/10] t3701: adjust difffilter test

From: Johannes Schindelin <johannes.schindelin@gmx.de>

In 42f7d45428e (add--interactive: detect bogus diffFilter output, 2018-03-03), we added a test case that verifies that the diffFilter feature complains appropriately when the output is too short.

In preparation for the upcoming change where the built-in `add -p` is taught to respect that setting, let's adjust that test a little. The problem is that `echo too-short` is configured as diffFilter, and it does not read the `stdin`. When calling it through `pipe_command()`, it is therefore possible that we try to feed the `diff` to it while it is no longer listening, and we receive a `SIGPIPE`.

The Perl code apparently handles this in a way similar to an end-of-file, but taking a step back, we realize that a diffFilter that does not even _look_ at its standard input is very unrealistic. The entire point of this feature is to transform the diff, not to ignore it altogether.

So let's modify the test case to reflect that insight: instead of printing some bogus text, let's use a diffFilter that deletes the first line of the diff instead.

This still tests for the same thing, but it does not confuse the built-in `add -p` with that `SIGPIPE`.

Helped-by: SZEDER Gábor <szeder.dev@gmail.com>
Helped-by: Jeff King <peff@peff.net>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
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 t/t3701-add-interactive.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)