Implement unit testing and keep .obs and .var in correct_scanpy()

Test output passed, will merge:
=========================================================================== test session starts ============================================================================
platform linux -- Python 3.7.4, pytest-5.4.1, py-1.8.0, pluggy-0.13.0
rootdir: /afs/csail.mit.edu/u/b/brianhie/research/scanorama
plugins: arraydiff-0.3, doctestplus-0.4.0, openfiles-0.4.0, remotedata-0.3.2
collected 3 items

tests/test_scanorama.py ...                                                                                                                                          [100%]

============================================================================= warnings summary =============================================================================
/data/cb/brianhie/anaconda3/lib/python3.7/site-packages/intervaltree/intervaltree.py:37
  /data/cb/brianhie/anaconda3/lib/python3.7/site-packages/intervaltree/intervaltree.py:37: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
    class IntervalTree(collections.MutableSet):

/data/cb/brianhie/anaconda3/lib/python3.7/site-packages/nose/importer.py:12
  /data/cb/brianhie/anaconda3/lib/python3.7/site-packages/nose/importer.py:12: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
    from imp import find_module, load_module, acquire_lock, release_lock

-- Docs: https://docs.pytest.org/en/latest/warnings.html
====================================================================== 3 passed, 2 warnings in 3.18s =======================================================================
brianhie / scanorama

Implement unit testing and keep .obs and .var in correct_scanpy() #77
