Fix unit tests

The only unit test that was actually giving me an error was test_filters.py which now is fixed and the problem lied in the order in which the arguments were defined in the init function of FilterBase. All of the other errors appeared because of namespace issues. test_structure_tenson.py doesn't raise any error for me. Lastly I reduced run time for test_downloader.py from 4 minutes to 2 minutes.