Do not validate test requests using absolute URLs

The response validation in the fetch method of AsyncOpenAPITestCase is
intended for requests made to the application under test only, and must
not be executed on requests made to other services using absolute URLs.

tests/test_testing.py

@@ -106,6 +106,9 @@ class IncorrectResponseTests(BaseTestCase):
             self.fetch("/resource")
         self.assertEqual("400", context.exception.http_status)
 
+    def test_errors_not_raised_when_using_absolute_url(self) -> None:
+        self.fetch(self.get_url("/resource"))
+
 
 class RaiseErrorTests(BaseTestCase):
     spec_dict = spec(

tornado_openapi3/testing.py

@@ -87,7 +87,13 @@ class AsyncOpenAPITestCase(tornado.testing.AsyncHTTPTestCase):
         fails, an :class:`openapi_core.exceptions.OpenAPIError` will be raised
         describing the failure.
 
+        If the path begins with http:// or https://, it will be treated as a
+        full URL and will be fetched as-is, and no validation will occur.
+
         """
+        if path.lower().startswith(("http://", "https://")):
+            return super().fetch(path, raise_error=raise_error, **kwargs)
+
         response = super().fetch(path, raise_error=False, **kwargs)
         result = self.validator.validate(response)
         result.raise_for_errors()