LIBFCREPO-944. Pinned "watchdog" package to v0.10.3

v0.10.4 of the "watchdog" package had an extensive update to the
"fsevent" observer, which appears to have broken functionality the
Plastron InboxWatcher relies on
(gorakhargosh/watchdog#680)

The problem still exists in the latest current watchdog version
(v1.0.2), so pinning the "watchdog" package to v0.10.3 is the simplest
fix for now.

The "tests/stomp/test_inbox_watcher.py" passed when using v0.10.3, and
fails in v0.10.4 and later, so it can be used to gauge whether
"watchdog" is performing as expected by Plastron.

https://issues.umd.edu/browse/LIBFCREPO-944

requirements.txt

@@ -12,5 +12,5 @@ Pillow>=6.2.2
 pytest
 stomp.py==4.1.21
 numpy==1.17.1
-watchdog>=0.10.2
+watchdog==0.10.3
 bagit~=1.7.0

setup.py

@@ -85,7 +85,7 @@
         'requests',
         'setuptools',
         'stomp.py',
-        'watchdog>=0.10.2'
+        'watchdog==0.10.3'
     ],
     python_requires='>=3.6',
 

tests/stomp/test_inbox_watcher.py

@@ -0,0 +1,52 @@
+from plastron.stomp.inbox_watcher import InboxWatcher
+from plastron.stomp.messages import MessageBox
+
+from unittest.mock import patch
+import tempfile
+import os
+import time
+
+from contextlib import contextmanager
+
+def test_new_file_in_inbox():
+    with tempfile.TemporaryDirectory() as inbox_dirname:
+        with patch('plastron.stomp.listeners.CommandListener') as mock_command_listener:
+            # Mock "process_message" and use to verify that CommandListener
+            # is called (when a file is created in the inbox).
+            mock_method = mock_command_listener.process_message
+
+            with inbox_watcher(inbox_dirname, mock_command_listener):
+                create_test_file(inbox_dirname)
+
+                wait_until_called(mock_method)
+
+                mock_method.assert_called_once()
+
+# Utility methods
+
+@contextmanager
+def inbox_watcher(inbox_dirname, mock_command_listener):
+    inbox = MessageBox(inbox_dirname)
+    inbox_watcher = InboxWatcher(mock_command_listener, inbox)
+    inbox_watcher.start()
+
+    try:
+        yield
+    finally:
+        inbox_watcher.stop()
+
+def create_test_file(inbox_dirname):
+    temp_file = open(os.path.join(inbox_dirname, 'test_new_file'),'w')
+    temp_file.write("test:test")
+    temp_file.close()
+
+def wait_until_called(mock_method, interval=0.1, timeout=5):
+    '''Polls at the given interval until either the mock_method is called
+       or the timeout occurs.'''
+    # Inspired by https://stackoverflow.com/a/36040926
+    start = time.time()
+    while not mock_method.called and time.time() - start < timeout:
+        time.sleep(interval)
+
+
+