t7600-merge: Use test_expect_failure to test option parsing

It used plain 'if git merge ...', which hides a segfault. The test does not pass.

Signed-off-by: Johannes Sixt <johannes.sixt@telecom.at>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7600-merge.sh

@@ -222,36 +222,12 @@ test_expect_success 'setup' '
 test_debug 'gitk --all'
 
 test_expect_success 'test option parsing' '
-	if git merge -$ c1
-	then
-		echo "[OOPS] -$ accepted"
-		false
-	fi &&
-	if git merge --no-such c1
-	then
-		echo "[OOPS] --no-such accepted"
-		false
-	fi &&
-	if git merge -s foobar c1
-	then
-		echo "[OOPS] -s foobar accepted"
-		false
-	fi &&
-	if git merge -s=foobar c1
-	then
-		echo "[OOPS] -s=foobar accepted"
-		false
-	fi &&
-	if git merge -m
-	then
-		echo "[OOPS] missing commit msg accepted"
-		false
-	fi &&
-	if git merge
-	then
-		echo "[OOPS] missing commit references accepted"
-		false
-	fi
+	test_must_fail git merge -$ c1 &&
+	test_must_fail git merge --no-such c1 &&
+	test_must_fail git merge -s foobar c1 &&
+	test_must_fail git merge -s=foobar c1 &&
+	test_must_fail git merge -m &&
+	test_must_fail git merge
 '
 
 test_expect_success 'merge c0 with c1' '