for-each-ref: explicitly test no matches

The for-each-ref builtin can take a list of ref patterns, but if none
match, it still succeeds (but with no output). Add an explicit test that
demonstrates that behavior.

Signed-off-by: Derrick Stolee <derrickstolee@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
diff --git a/t/t6300-for-each-ref.sh b/t/t6300-for-each-ref.sh
index a58053a..6614469 100755
--- a/t/t6300-for-each-ref.sh
+++ b/t/t6300-for-each-ref.sh
@@ -1501,4 +1501,17 @@
 	test_cmp expect actual
 '
 
+test_expect_success 'git for-each-ref with non-existing refs' '
+	cat >in <<-EOF &&
+	refs/heads/this-ref-does-not-exist
+	refs/tags/bogus
+	EOF
+
+	git for-each-ref --format="%(refname)" --stdin <in >actual &&
+	test_must_be_empty actual &&
+
+	xargs git for-each-ref --format="%(refname)" <in >actual &&
+	test_must_be_empty actual
+'
+
 test_done