Added tests for wave_unit_catcher()
Issue #929: Added a few test cases
Issuee #929: Changed the test for wave_unit_catcher() by including numpy's allclose
Issue #929: Changed the values in the test_values list in the test for wave_unit_catcher()
Issue #929: Checking type of hek results using isinstance()
Merge pull request #936 from rajul-iitkgp/master

Issue #929: Added a few test cases for sunpy.net.hek2vso