tests: fix StreamWorker test leading to bad Engine state (#502)

An unconfigured StreamWorker does not have streams to register in the
engine, so when registered, it stays until it is explicitly aborted. To
make that worse, it is using a 'fanout slot' and if the Engine's fanout
is too low, it can lead to the engine run loop exiting prematurely. This
is not a case handled very well by the Engine. See #497 for more details
about the problem.

In the meantime, we fix the test to exit with a clean engine state.

Fixes #488.

Author: thiell

tests/StreamWorkerTest.py

@@ -21,7 +21,13 @@ def test_001_empty(self):
         """test empty StreamWorker"""
         # that makes no sense but well...
         # handler=None is supported by base Worker class
-        self.run_worker(StreamWorker(handler=None))
+        worker = StreamWorker(handler=None)
+        self.run_worker(worker)
+        # GH Issue #488:
+        # An unconfigured engine client does not abort by itself...
+        worker.abort()
+        # Check that we are in a clean state now
+        self.assertEqual(len(task_self()._engine._clients), 0)
 
     def test_002_pipe_readers(self):
         """test StreamWorker bound to several pipe readers"""