🧪 Test unhandled internal exceptions in workers

This is to ensure that such exceptions don't crash the worker threads
starving the server of the processing resources.

cheroot/test/test_conn.py

@@ -875,6 +875,89 @@ def _trigger_scary_exc(_req, _resp):
  )
 
 
+def test_remains_alive_post_unhandled_exception(
+ mocker,
+ monkeypatch,
+ test_client,
+ testing_server,
+ wsgi_server_thread,
+):
+ """Ensure worker threads are resillient to unhandled exceptions."""
+
+ class ScaryCrash(BaseException): # noqa: WPS418, WPS431
+ """A simulated crash during HTTP parsing."""
+
+ _orig_read_request_line = (
+ test_client.server_instance.
+ ConnectionClass.RequestHandlerClass.
+ read_request_line
+ )
+
+ def _read_request_line(self):
+ _orig_read_request_line(self)
+ raise ScaryCrash(666)
+
+ monkeypatch.setattr(
+ test_client.server_instance.ConnectionClass.RequestHandlerClass,
+ 'read_request_line',
+ _read_request_line,
+ )
+
+ server_connection_close_spy = mocker.spy(
+ test_client.server_instance.ConnectionClass,
+ 'close',
+ )
+
+ # NOTE: The initial worker thread count is 10.
+ assert len(testing_server.requests._threads) == 10
+
+ test_client.get_connection().send(b'GET / HTTP/1.1')
+
+ # NOTE: This spy ensure the log entry gets recorded before we're testing
+ # NOTE: them and before server shutdown, preserving their order and making
+ # NOTE: the log entry presence non-flaky.
+ while not server_connection_close_spy.called: # noqa: WPS328
+ pass
+
+ # NOTE: This checks for whether there's any crashed threads
+ while testing_server.requests.idle < 10: # noqa: WPS328
+ pass
+ assert len(testing_server.requests._threads) == 10
+ assert all(
+ worker_thread.is_alive()
+ for worker_thread in testing_server.requests._threads
+ )
+ testing_server.interrupt = SystemExit('test requesting shutdown')
+ assert not testing_server.requests._threads
+ wsgi_server_thread.join() # no extra logs upon server termination
+
+ actual_log_entries = testing_server.error_log.calls[:]
+ testing_server.error_log.calls.clear() # prevent post-test assertions
+
+ expected_log_entries = (
+ (
+ logging.ERROR,
+ '^Unhandled error while processing an incoming connection '
+ r'ScaryCrash\(666\)$',
+ ),
+ (
+ logging.INFO,
+ '^SystemExit raised: shutting down$',
+ ),
+ )
+
+ assert len(actual_log_entries) == len(expected_log_entries)
+
+ for ( # noqa: WPS352
+ (expected_log_level, expected_msg_regex),
+ (actual_msg, actual_log_level, _tb),
+ ) in zip(expected_log_entries, actual_log_entries):
+ assert expected_log_level == actual_log_level
+ assert _matches_pattern(expected_msg_regex, actual_msg) is not None, (
+ f'{actual_msg !r} does not match {expected_msg_regex !r}'
+ )
+
+
 @pytest.mark.parametrize(
  'timeout_before_headers',
  (