implement test_value_error

tests/test_dataDistribution.py

@@ -63,7 +63,15 @@ class TestDataDistribution(unittest.TestCase):
         self.assertTrue(max_osd_total_folder_size > osd_capacity)
 
     def test_value_error(self):
-        pass
+        distribution = dataDistribution.DataDistribution()
+        distribution.add_osd_list(create_test_osd_list(1))
+        try:
+            distribution.add_folders(create_test_folder_list(1, 1),
+                                     random_osd_assignment=True,
+                                     ignore_osd_capacities=False)
+        except ValueError:
+            return # expect value error
+        self.fail("expect value error!")
 
     def test_random_distribution_respecting_capacities(self):
         pass