Increase test coverage

[chrisburr]

After #1 the test coverage is sitting at around 35%. It would be nice to get this a bit higher, especially if #2 is implemented.

For reference:

---------- coverage: platform darwin, python 3.8.1-final-0 -----------
Name                   Stmts   Miss  Cover   Missing
----------------------------------------------------
diraccfg/__init__.py       3      0   100%
diraccfg/__main__.py      47      0   100%
diraccfg/cfg.py          563    400    29%   15, 19, 24-29, 45, 51, 56, 97, 99-105, 111-113, 125-127, 142, 144-150, 175, 182-184, 192-194, 205-216, 229-250, 264, 278, 289-298, 309-318, 326, 336-344, 362-379, 393-436, 444-451, 464-470, 487-494, 511-524, 537-561, 572-575, 582-583, 589, 597, 605, 611, 617-624, 637-638, 650-653, 664-684, 693-700, 712-736, 751-815, 825-882, 895-899, 944-948, 955-963, 973-981
----------------------------------------------------
TOTAL                    613    400    35%