Add the quote_plus call in the test.
diff --git a/Lib/test/test_urllib.py b/Lib/test/test_urllib.py
index ac02374..c6dae17 100644
--- a/Lib/test/test_urllib.py
+++ b/Lib/test/test_urllib.py
@@ -490,6 +490,7 @@
         result = urllib.parse.quote(partial_quote)
         self.assertEqual(expected, result,
                          "using quote(): %r != %r" % (expected, result))
+        result = urllib.parse.quote_plus(partial_quote)
         self.assertEqual(expected, result,
                          "using quote_plus(): %r != %r" % (expected, result))