Fix tests with Twisted trunk

AGENTS.md

@@ -0,0 +1,14 @@
+# Contributor Guide
+
+Synapse is a Python application that has Rust modules via pyo3 for performance.
+
+## Dev Environment Tips
+- Source code is primarily in `synapse/`, tests are in `tests/`.
+- Run `poetry install --dev` to install development python dependencies. This will also build and install the Synapse rust code.
+- Use `./scripts-dev/lint.sh` to lint the codebase (this attempts to fix issues as well). This should be run and produce no errors before every commit.
+
+## Testing Instructions
+- Find the CI plan in the .github/workflows folder.
+- Use `poetry run trial tests` to run all unit tests, or `poetry run trial tests.metrics.test_phone_home_stats.PhoneHomeStatsTestCase` (for example) to run a single test case. The commit should pass all tests before you merge.
+- Some typing warnings are expected currently. Fix any test or type *errors* until the whole suite is green.
+- Add or update relevant tests for the code you change, even if nobody asked.

tests/http/federation/test_matrix_federation_agent.py

@@ -84,6 +84,15 @@ def setUp(self) -> None:
 
         self.tls_factory = FederationPolicyForHTTPS(config)
 
+        # ensure any proxy settings from the environment do not interfere with
+        # the tests. In some execution environments (like CI or the test
+        # runner's container) `https_proxy` or `http_proxy` may be preset which
+        # would cause the agent to attempt to proxy outbound connections.
+        for var in ("http_proxy", "https_proxy", "HTTP_PROXY", "HTTPS_PROXY"):
+            if var in os.environ:
+                old = os.environ.pop(var)
+                self.addCleanup(os.environ.__setitem__, var, old)
+
         self.well_known_cache: TTLCache[bytes, Optional[bytes]] = TTLCache(
             "test_cache", timer=self.reactor.seconds
         )