test patch hunk editing with "commit -p -m"

Add (failing) tests: with commit changing the environment to let hooks
know that no editor will be used (by setting GIT_EDITOR to ":"), the
"edit hunk" functionality does not work (no editor is launched and the
whole hunk is committed).
Signed-off-by: NBenoit Pierre <benoit.pierre@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t7514-commit-patch.sh

+#!/bin/sh
+
+test_description='hunk edit with "commit -p -m"'
+. ./test-lib.sh
+
+if ! test_have_prereq PERL
+then
+	skip_all="skipping '$test_description' tests, perl not available"
+	test_done
+fi
+
+test_expect_success 'setup (initial)' '
+	echo line1 >file &&
+	git add file &&
+	git commit -m commit1
+'
+
+test_expect_failure 'edit hunk "commit -p -m message"' '
+	test_when_finished "rm -f editor_was_started" &&
+	rm -f editor_was_started &&
+	echo more >>file &&
+	echo e | env GIT_EDITOR=": >editor_was_started" git commit -p -m commit2 file &&
+	test -r editor_was_started
+'
+
+test_expect_failure 'edit hunk "commit --dry-run -p -m message"' '
+	test_when_finished "rm -f editor_was_started" &&
+	rm -f editor_was_started &&
+	echo more >>file &&
+	echo e | env GIT_EDITOR=": >editor_was_started" git commit -p -m commit3 file &&
+	test -r editor_was_started
+'
+
+test_done