Address peer review comments.

Signed-off-by: Michel Hidalgo <michel@ekumenlabs.com>

launch/test/launch/test_launch_service.py

@@ -14,15 +14,15 @@
 
 """Tests for the LaunchService class."""
 
-import asyncio
-import osrf_pycommon
 import queue
 import threading
 
 from launch import LaunchDescription
 from launch import LaunchService
 from launch.events import ExecutionComplete
 
+import osrf_pycommon
+
 
 def test_launch_service_constructors():
  """Test the constructors for LaunchService class."""
@@ -65,19 +65,25 @@ class MockEvent:
  assert ls._LaunchService__context._event_queue.qsize() == 2
  assert handled_events.qsize() == 0
 
+ # Spin up a background thread for testing purposes.
  def perform_test_sequence():
  # First event (after including description of event handler).
  handled_events.get(block=True, timeout=5.0)
  # Emit and then check for a second event.
  ls.emit_event(MockEvent())
  handled_events.get(block=True, timeout=5.0)
- # Shutdown (generates a third event) and join the thread.
+ # Shutdown (generates a third event).
  ls.shutdown()
 
- threading.Thread(target=perform_test_sequence).start()
+ t = threading.Thread(target=perform_test_sequence)
+ t.start()
 
+ # Run the launch service.
  assert ls.run(shutdown_when_idle=False) == 0
 
+ # Join background thread if still running.
+ t.join()
+
  # Check that the shutdown event was handled.
  handled_events.get(block=False)