def METHOD_NAME(self):
    """Property extensions is missing, the serializer must not be valid."""
    data = {}
    serializer = ExtensionSerializer(data=data)
    self.assertFalse(serializer.is_valid())
    self.assertIn("extensions", serializer.errors)
    error = serializer.errors.get("extensions").pop(0)
    self.assertEqual(error.code, "required")