more-generic testing hook

src/allmydata/storage/http_client.py

@@ -427,7 +427,7 @@ class StorageClient(object):
     _pool: HTTPConnectionPool
     _clock: IReactorTime
     # Are we running unit tests?
-    _test_mode: bool
+    _analyze_response: Callable[[IResponse], None] = lambda _: None
 
     def relative_url(self, path: str) -> DecodedURL:
         """Get a URL relative to the base URL."""
@@ -534,12 +534,7 @@ class StorageClient(object):
         response = await self._treq.request(
             method, url, headers=headers, timeout=timeout, **kwargs
         )
-
-        if self._test_mode and response.code != 404:
-            # We're doing API queries, HTML is never correct except in 404, but
-            # it's the default for Twisted's web server so make sure nothing
-            # unexpected happened.
-            assert get_content_type(response.headers) != "text/html"
+        self._analyze_response(response)
 
         return response
 

src/allmydata/test/test_storage_http.py

@@ -316,6 +316,17 @@ def result_of(d):
         + "This is probably a test design issue."
     )
 
+def response_is_not_html(response):
+    """
+    During tests, this is registered so we can ensure the web server
+    doesn't give us text/html.
+
+    HTML is never correct except in 404, but it's the default for
+    Twisted's web server so we assert nothing unexpected happened.
+    """
+    if response.code != 404:
+        assert get_content_type(response.headers) != "text/html"
+
 
 class CustomHTTPServerTests(SyncTestCase):
     """
@@ -342,7 +353,7 @@ class CustomHTTPServerTests(SyncTestCase):
             # fixed if https://github.com/twisted/treq/issues/226 were ever
             # fixed.
             clock=treq._agent._memoryReactor,
-            test_mode=True,
+            analyze_response=response_is_not_html,
         )
         self._http_server.clock = self.client._clock
 
@@ -560,7 +571,7 @@ class HttpTestFixture(Fixture):
             treq=self.treq,
             pool=None,
             clock=self.clock,
-            test_mode=True,
+            analyze_response=response_is_not_html,
         )
 
     def result_of_with_flush(self, d):
@@ -674,7 +685,7 @@ class GenericHTTPAPITests(SyncTestCase):
                 treq=StubTreq(self.http.http_server.get_resource()),
                 pool=None,
                 clock=self.http.clock,
-                test_mode=True,
+                analyze_response=response_is_not_html,
             )
         )
         with assert_fails_with_http_code(self, http.UNAUTHORIZED):