Fix the contains error message.

Author: Julian

jsonschema/_validators.py

@@ -127,7 +127,7 @@ def contains(validator, contains, instance, schema):
 
     if not any(validator.is_valid(element, contains) for element in instance):
         yield ValidationError(
-            "XXX"
+            "None of %r are valid under the given schema" % (instance,)
         )
 
 

jsonschema/tests/test_validators.py

@@ -368,6 +368,18 @@ def test_const(self):
         )
         self.assertIn("12 was expected", message)
 
+    def test_contains(self):
+        schema = {u"contains": {u"const": 12}}
+        message = self.message_for(
+            instance=[2, {}, []],
+            schema=schema,
+            cls=validators.Draft6Validator,
+        )
+        self.assertIn(
+            "None of [2, {}, []] are valid under the given schema",
+            message,
+        )
+
     def test_invalid_format_default_message(self):
         checker = FormatChecker(formats=())
         check_fn = mock.Mock(return_value=False)