improve javadoc for the MdmCommand.repo field.
add test helper method to assert commands ran without error.

questioning if this would be better served by rethinking returns as throwable -- the origins of all this as a port of an already-questionable python script are certainly still showing -- but punting on that for now.
rename method so overriding doesn't bork the intention of the junit Before annotation.
set up a release repo fixture for the add command test.
this test hits some of the code that needed the SystemReaderFilteringProxy workaround.  add that to the static initializer block for the test class.  wish there was a better way to correct that issue, but when third-party libraries hand you globals, you prepare to drown in lemonade for no discernable reason.