+        elif isinstance(expected, compat_str) and expected.startswith('contains:'):
+            got = got_dict.get(info_field)
+            contains_str = expected[len('contains:'):]
+            self.assertTrue(
+                isinstance(got, compat_str),
+                'Expected a %s object, but got %s for field %s' % (
+                    compat_str.__name__, type(got).__name__, info_field))
+            self.assertTrue(
+                contains_str in got,
+                'field %s (value: %r) should contain %r' % (info_field, got, contains_str))