diff --git a/sacred/optional.py b/sacred/optional.py
index <HASH>..<HASH> 100644
--- a/sacred/optional.py
+++ b/sacred/optional.py
@@ -13,6 +13,10 @@ class MissingDependencyMock(object):
         raise ImportError('Depends on missing "{}" package.'
                           .format(object.__getattribute__(self, 'depends_on')))
 
+    def __call__(self, *args, **kwargs):
+        raise ImportError('Depends on missing "{}" package.'
+                          .format(object.__getattribute__(self, 'depends_on')))
+
 
 try:
     import numpy as np
diff --git a/tests/conftest.py b/tests/conftest.py
index <HASH>..<HASH> 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -42,7 +42,7 @@ def pytest_generate_tests(metafunc):
     if 'example_test' in metafunc.fixturenames:
         examples = [f.strip('.py') for f in os.listdir(EXAMPLES_PATH)
                     if os.path.isfile(os.path.join(EXAMPLES_PATH, f)) and
-                    f.endswith('.py')]
+                    f.endswith('.py') and f != '__init__.py']
 
         sys.path.append(EXAMPLES_PATH)
         example_tests = []
MissingDependencyMock is now callable