Start test subprocess from the main thread, using an event queue to c…

…oordinate:

* Allow only a single instance of pytest to run at any time
* Queue up filesystem events while the tests are running
* Spool on dequeue instead of enqueue
* Simplify show_summary

pytest_watch/helpers.py

@@ -1,6 +1,12 @@
 import os
 import subprocess
 import sys
+from time import sleep
+
+try:
+    from queue import Empty
+except ImportError:
+    from Queue import Empty
 
 
 is_windows = sys.platform == 'win32'
@@ -21,6 +27,25 @@ def clear():
     subprocess.call('cls' if is_windows else 'clear', shell=True)
 
 
+def dequeue_all(queue, spool=False):
+    """
+    Empties the specified queue into a list, optionally with spool time.
+    """
+    items = []
+    while True:
+        try:
+            while True:
+                items.append(queue.get_nowait())
+        except Empty:
+            # If spooling, wait a moment and check for new items
+            if spool:
+                sleep(0.2)
+                if not queue.empty():
+                    continue
+            break
+    return items
+
+
 def samepath(left, right):
     """
     Determines whether two paths are the same.