fix: get tests passing on plucky (#290)

Twisted changed a little bit - it used to run `cleanFailure` on
`Failure` instances in the `defer` code but no longer does in the
version available in plucky (python3-twisted 24.10).

This change does `cleanFailure` in the `FakeReactor` we use for some
tests. This allows tests that rely on catching and flushing `Failure`s
to succeed.

landscape/client/broker/tests/test_transport.py

@@ -193,16 +193,10 @@ def test_ssl_verification_negative(self):
             message_api=b"X.Y",
         )
 
-        def got_result(ignored):
+        def got_result(failure):
             self.assertIs(r.request, None)
             self.assertIs(r.content, None)
-            logfile_value = self.logfile.getvalue()
-            # pycurl error messages vary by version.
-            # First is for <= noble, second for > noble.
-            self.assertTrue(
-                "server certificate verification failed" in logfile_value
-                or "SSL certificate problem" in logfile_value,
-            )
+            self.assertEqual(failure.value.error_code, 60)
 
         result.addErrback(got_result)
         return result

landscape/lib/testing.py

@@ -685,7 +685,15 @@ def fake():
             # because the call might cancel it!
             call._data = self.call_later(seconds, fake)._data
             try:
-                f(*args, **kwargs)
+                deferred = f(*args, **kwargs)
+
+                if (
+                    hasattr(deferred, "result")
+                    and isinstance(deferred.result, Failure)
+                ):
+                    # Required for failures to get GC'd and properly flushed.
+                    # Twisted did this for us in versions < 24.10.
+                    deferred.result.cleanFailure()
             except Exception:
                 if call.active:
                     self.cancel_call(call)