git-diff: add a test for git diff --quiet -w

This patch adds two test cases for:

6977c25 git diff --quiet -w: check and report the status

Signed-off-by: Larry D'Anna <larry@elder-gods.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4017-diff-retval.sh

@@ -5,6 +5,9 @@ test_description='Return value of diffs'
 . ./test-lib.sh
 
 test_expect_success 'setup' '
+	echo "1 " >a &&
+	git add . &&
+	git commit -m zeroth &&
 	echo 1 >a &&
 	git add . &&
 	git commit -m first &&
@@ -13,6 +16,18 @@ test_expect_success 'setup' '
 	git commit -a -m second
 '
 
+test_expect_success 'git diff --quiet -w  HEAD^^ HEAD^' '
+	git diff --quiet -w HEAD^^ HEAD^
+'
+
+test_expect_success 'git diff --quiet HEAD^^ HEAD^' '
+	test_must_fail git diff --quiet HEAD^^ HEAD^
+'
+
+test_expect_success 'git diff --quiet -w  HEAD^ HEAD' '
+	test_must_fail git diff --quiet -w HEAD^ HEAD
+'
+
 test_expect_success 'git diff-tree HEAD^ HEAD' '
 	git diff-tree --exit-code HEAD^ HEAD
 	test $? = 1