diff --git a/src/test_ddns_update.py b/src/test_ddns_update.py
new file mode 100644
index 0000000..a091beb
--- /dev/null
+++ b/src/test_ddns_update.py
@@ -0,0 +1,20 @@
+import unittest
+from .ddns_update import response_successful
+
+class TestDdnsUpdate(unittest.TestCase):
+
+    def test_response_successful(self):
+        self.assertTrue(response_successful("good"))
+        self.assertTrue(response_successful("good 1.2.3.4"))
+        self.assertTrue(response_successful("good abcd:abcd:abcd:abcd:abcd:abcd:abcd:abcd"))
+        self.assertTrue(response_successful("nochg"))
+        self.assertTrue(response_successful("nochg 1.2.3.4"))
+        self.assertTrue(response_successful("nochg abcd:abcd:abcd:abcd:abcd:abcd:abcd:abcd"))
+        self.assertFalse(response_successful("notfqdn"))
+        self.assertFalse(response_successful("nohost"))
+        self.assertFalse(response_successful("numhost"))
+        self.assertFalse(response_successful("abuse"))
+        self.assertFalse(response_successful("badagent"))
+        self.assertFalse(response_successful("dnserr"))
+        self.assertFalse(response_successful("911"))
+