t7604-merge-custom-message: shift expected output creation

Squash in a minor rename too.

Signed-off-by: Tay Ray Chuan <rctay89@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7604-merge-custom-message.sh

@@ -6,6 +6,10 @@ Testing merge when using a custom message for the merge commit.'
 
 . ./test-lib.sh
 
+create_merge_msgs() {
+	echo >exp.subject "custom message"
+}
+
 test_expect_success 'setup' '
 	echo c0 > c0.c &&
 	git add c0.c &&
@@ -19,16 +23,16 @@ test_expect_success 'setup' '
 	echo c2 > c2.c &&
 	git add c2.c &&
 	git commit -m c2 &&
-	git tag c2
+	git tag c2 &&
+	create_merge_msgs
 '
 
 
 test_expect_success 'merge c2 with a custom message' '
 	git reset --hard c1 &&
-	echo >expected "custom message" &&
-	git merge -m "custom message" c2 &&
+	git merge -m "$(cat exp.subject)" c2 &&
 	git cat-file commit HEAD | sed -e "1,/^$/d" >actual &&
-	test_cmp expected actual
+	test_cmp exp.subject actual
 '
 
 test_done