when JSON data file is missing visibly fail

* creates a fake test function that raises ValueError

ddt.py

@@ -87,7 +87,14 @@ def ddt(cls):
         """
         cls_path = os.path.abspath(inspect.getsourcefile(cls))
         data_file_path = os.path.join(os.path.dirname(cls_path), file_attr)
-        if os.path.exists(data_file_path):
+
+        def _raise_ve(*args):
+            raise ValueError("%s does not exist" % file_attr)
+
+        if os.path.exists(data_file_path) is False:
+            test_name = "{0}_{1}".format(name, "error")
+            setattr(cls, test_name, feed_data(_raise_ve, None))
+        else:
             data = json.loads(open(data_file_path).read())
             for elem in data:
                 if isinstance(data, dict):

test/test_functional.py

@@ -1,7 +1,7 @@
 import os
 import json
 from ddt import ddt, data, file_data
-from nose.tools import assert_equal, assert_is_not_none
+from nose.tools import assert_equal, assert_is_not_none, assert_raises
 
 
 @ddt
@@ -26,6 +26,18 @@ class FileDataDummy(object):
         return value
 
 
+@ddt
+class FileDataMissingDummy(object):
+    """
+    Dummy class to test the file_data decorator on when
+    JSON file is missing
+    """
+
+    @file_data("test_data_dict_missing.json")
+    def test_something_again(self, value):
+        return value
+
+
 def test_data_decorator():
     """
     Test the ``data`` method decorator
@@ -139,6 +151,19 @@ def test_feed_data_file_data():
     assert_equal(set(values), set([10, 12, 15, 15, 12, 50]))
 
 
+def test_feed_data_file_data_missing_json():
+    """
+    Test that a ValueError is raised
+    """
+    tests = filter(is_test, FileDataMissingDummy.__dict__)
+
+    values = []
+    obj = FileDataMissingDummy()
+    for test in tests:
+        method = getattr(obj, test)
+        assert_raises(ValueError, method)
+
+
 def test_ddt_data_name_attribute():
     """
     Test the ``__name__`` attribute handling of ``data`` items with ``ddt``