rm tests: actually test for SIGPIPE in SIGPIPE test

Change a test initially added in 50cd31c (t3600: comment on
inducing SIGPIPE in `git rm`, 2019-11-27) to explicitly test for
SIGPIPE using a pattern initially established in 7559a1b (unblock
and unignore SIGPIPE, 2014-09-18).

The problem with using that pattern is that it requires us to skip the
test on MINGW[1]. If we kept the test with its initial semantics[2]
we'd get coverage there, at the cost of not checking whether we
actually had SIGPIPE outside of MinGW.

Arguably we should just remove this test. Between the test added in
7559a1b and the change made in 12e0437 (common-main: call
restore_sigpipe_to_default(), 2016-07-01) it's a bit arbitrary to only
check this for "git rm".

But in lieu of having wider test coverage for other "git" subcommands
let's refactor this to explicitly test for SIGPIPE outside of MinGW,
and then just that we remove the ".git/index.lock" (as before) on all
platforms.

1. https://lore.kernel.org/git/[email protected]/
2. 0693f9d (Make sure lockfiles are unlocked when dying on SIGPIPE,
   2008-12-18)

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

t/t3600-rm.sh

@@ -240,7 +240,7 @@ test_expect_success 'refresh index before checking if it is up-to-date' '
 	test_path_is_missing frotz/nitfol
 '
 
-test_expect_success 'choking "git rm" should not let it die with cruft' '
+choke_git_rm_setup() {
 	git reset -q --hard &&
 	test_when_finished "rm -f .git/index.lock && git reset -q --hard" &&
 	i=0 &&
@@ -249,12 +249,24 @@ test_expect_success 'choking "git rm" should not let it die with cruft' '
 	do
 		echo "100644 $hash 0	some-file-$i"
 		i=$(( $i + 1 ))
-	done | git update-index --index-info &&
+	done | git update-index --index-info
+}
+
+test_expect_success 'choking "git rm" should not let it die with cruft (induce SIGPIPE)' '
+	choke_git_rm_setup &&
 	# git command is intentionally placed upstream of pipe to induce SIGPIPE
 	git rm -n "some-file-*" | : &&
 	test_path_is_missing .git/index.lock
 '
 
+
+test_expect_success !MINGW 'choking "git rm" should not let it die with cruft (induce and check SIGPIPE)' '
+	choke_git_rm_setup &&
+	OUT=$( ((trap "" PIPE; git rm -n "some-file-*"; echo $? 1>&3) | :) 3>&1 ) &&
+	test_match_signal 13 "$OUT" &&
+	test_path_is_missing .git/index.lock
+'
+
 test_expect_success 'Resolving by removal is not a warning-worthy event' '
 	git reset -q --hard &&
 	test_when_finished "rm -f .git/index.lock msg && git reset -q --hard" &&