Introduced logging in case of plugin load error

force_bdss/bdss_application.py

-from stevedore import extension
+import functools
+import logging
+
+from stevedore.extension import ExtensionManager
 from stevedore.exception import NoMatches
 
 from envisage.api import Application
@@ -34,18 +37,31 @@ class BDSSApplication(Application):
         else:
             plugins.append(CoreMCODriver())
 
-        mgr = extension.ExtensionManager(
+
+
+        mgr = ExtensionManager(
             namespace='force.bdss.extensions',
-            invoke_on_load=True
+            invoke_on_load=True,
+            on_load_failure_callback=functools.partial(_load_failure_callback)
         )
 
-        def import_extensions(ext):
-            print("Found extension {}".format(ext.name))
-            plugins.append(ext.obj)
-
         try:
-            mgr.map(import_extensions)
+            mgr.map(functools.partial(_import_extensions, plugins))
         except NoMatches:
-            print("No extensions found")
+            logging.info("No extensions found")
 
         super(BDSSApplication, self).__init__(plugins=plugins)
+
+
+def _import_extensions(plugins, ext):
+    logging.info("Found extension {}".format(ext.obj))
+    plugins.append(ext.obj)
+
+
+def _load_failure_callback(plugins, manager, entry_point, exception):
+    """Reports failure to load a module through stevedore.
+    """
+    logging.error(
+        "Unable to load plugin {}. Exception: {}. Message: {}".format(
+            entry_point, exception.__class__.__name__, exception)
+    )

force_bdss/tests/test_bdss_application.py

+import unittest
+import testfixtures
+
+from force_bdss.bdss_application import (
+    BDSSApplication,
+    _load_failure_callback,
+    _import_extensions
+)
+
+try:
+    import mock
+except ImportError:
+    from unittest import mock
+
+
+class TestBDSSApplication(unittest.TestCase):
+    def test_initialization(self):
+        app = BDSSApplication(False, "foo/bar")
+        self.assertFalse(app.evaluate)
+        self.assertEqual(app.workflow_filepath, "foo/bar")
+
+    def test_extension_load_failure(self):
+        plugins = []
+        with testfixtures.LogCapture() as log:
+            _load_failure_callback(plugins,
+                                   mock.Mock(),
+                                   "foo",
+                                   Exception("hello"))
+
+        log.check(
+            ('root', 'ERROR', "Unable to load plugin foo. Exception: "
+                              "Exception. Message: hello")
+        )
+        self.assertEqual(plugins, [])

requirements/dev_requirements.txt

 flake8
 coverage
 mock
+testfixtures