diff --git a/helpers_test.go b/helpers_test.go
new file mode 100644
index 0000000..44e2cc5
--- /dev/null
+++ b/helpers_test.go
@@ -0,0 +1,49 @@
+// Copyright (C) 2016 Opsmate, Inc.
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License, v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+//
+// This software is distributed WITHOUT A WARRANTY OF ANY KIND.
+// See the Mozilla Public License for details.
+
+package certspotter
+
+import (
+	"testing"
+)
+
+func doWildcardTest (t *testing.T, dnsName string, wildcard string, expected bool) {
+	if MatchesWildcard(dnsName, wildcard) != expected {
+		t.Errorf("MatchesWildcard(%q, %q) != %v", dnsName, wildcard, expected)
+	}
+}
+
+func TestMatchesWildcard(t *testing.T) {
+	doWildcardTest(t, "", "", true)
+	doWildcardTest(t, "example.com", "example.com", true)
+	doWildcardTest(t, "example.org", "example.com", false)
+	doWildcardTest(t, "example.com", "", false)
+	doWildcardTest(t, "", "example.com", false)
+	doWildcardTest(t, "", "*.example.com", false)
+	doWildcardTest(t, "", "exam*ple.com", false)
+	doWildcardTest(t, "", "exam*ple.co*m", false)
+	doWildcardTest(t, "example.org", "example.com", false)
+	doWildcardTest(t, "example.org", "*.example.com", false)
+	doWildcardTest(t, "example.org", "exam*ple.com", false)
+	doWildcardTest(t, "example.org", "exam*ple.co*m", false)
+	doWildcardTest(t, "example.com", "*.example.com", false)
+	doWildcardTest(t, "www.example.com", "*.example.com", true)
+	doWildcardTest(t, "", "*", true)
+	doWildcardTest(t, "", "****", true)
+	doWildcardTest(t, "a", "****", true)
+	doWildcardTest(t, "a", "*", true)
+	doWildcardTest(t, "a", "****", true)
+	doWildcardTest(t, "abcd", "****", true)
+	doWildcardTest(t, "abcdef", "****", true)
+	doWildcardTest(t, "www-example.com", "*-example.com", true)
+	doWildcardTest(t, "www-example-www.com", "*-example-*.com", true)
+	doWildcardTest(t, "examplecom", "example*", true)
+	doWildcardTest(t, "example.com", "example*", false)
+	doWildcardTest(t, "examplea.com", "example*", false)
+}