t3508: add check_head_differs_from() helper function and use it

In a test like:

test "$(git rev-parse --verify HEAD)" != "$(git rev-parse --verify fourth)"

the --verify does not accomplish much, since the exit status of
git rev-parse is not propagated to test. So it is more robust to
define and use the helper functions check_head_differs_from() and
check_head_equals() as done by this patch.

Suggested-by: Jonathan Nieder <jrnieder@gmail.com>
Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: chriscool

t/t3508-cherry-pick-many-commits.sh

@@ -4,6 +4,18 @@ test_description='test cherry-picking many commits'
 
 . ./test-lib.sh
 
+check_head_differs_from() {
+	head=$(git rev-parse --verify HEAD) &&
+	arg=$(git rev-parse --verify "$1") &&
+	test "$head" != "$arg"
+}
+
+check_head_equals() {
+	head=$(git rev-parse --verify HEAD) &&
+	arg=$(git rev-parse --verify "$1") &&
+	test "$head" = "$arg"
+}
+
 test_expect_success setup '
 	echo first > file1 &&
 	git add file1 &&
@@ -36,7 +48,7 @@ test_expect_success 'cherry-pick first..fourth works' '
 	git diff --quiet other &&
 	git diff --quiet HEAD other &&
 	test_cmp expected actual &&
-	test "$(git rev-parse --verify HEAD)" != "$(git rev-parse --verify fourth)"
+	check_head_differs_from fourth
 '
 
 test_expect_success 'cherry-pick --strategy resolve first..fourth works' '
@@ -53,7 +65,7 @@ test_expect_success 'cherry-pick --strategy resolve first..fourth works' '
 	git diff --quiet other &&
 	git diff --quiet HEAD other &&
 	test_cmp expected actual &&
-	test "$(git rev-parse --verify HEAD)" != "$(git rev-parse --verify fourth)"
+	check_head_differs_from fourth
 '
 
 test_expect_success 'cherry-pick --ff first..fourth works' '
@@ -63,7 +75,7 @@ test_expect_success 'cherry-pick --ff first..fourth works' '
 	git cherry-pick --ff first..fourth &&
 	git diff --quiet other &&
 	git diff --quiet HEAD other &&
-	test "$(git rev-parse --verify HEAD)" = "$(git rev-parse --verify fourth)"
+	check_head_equals fourth
 '
 
 test_expect_success 'cherry-pick -n first..fourth works' '
@@ -113,7 +125,7 @@ test_expect_success 'cherry-pick -3 fourth works' '
 	git cherry-pick -3 fourth &&
 	git diff --quiet other &&
 	git diff --quiet HEAD other &&
-	test "$(git rev-parse --verify HEAD)" != "$(git rev-parse --verify fourth)"
+	check_head_differs_from fourth
 '
 
 test_expect_success 'cherry-pick --stdin works' '
@@ -123,7 +135,7 @@ test_expect_success 'cherry-pick --stdin works' '
 	git rev-list --reverse first..fourth | git cherry-pick --stdin &&
 	git diff --quiet other &&
 	git diff --quiet HEAD other &&
-	test "$(git rev-parse --verify HEAD)" != "$(git rev-parse --verify fourth)"
+	check_head_differs_from fourth
 '
 
 test_done