Split the one monolithic test for basic.py into several files
* Split test_basic.py along categories.
This is preliminary to get a handle on things. Eventually we may want
to further split it so each file is only testing a single function.
* Cleanup unused imports from splitting test_basic.py
* Port atomic_move test to pytest.
Working on getting rid of need to maintain procenv
* Split a test of symbolic_mode_to_octal to follow unittest best practices
Each test should only invoke the function under test once
* Port test_argument_spec to pytest.
* Fix suboptions failure
