Introduce Parallel Test Suite Execution and Measure Benefits

[gkapfham]

The existing test suite for GatorGroup may take too long to run, especially as we start to add test cases for new algorithms and features. It would be ideal if we could reduce this execution time to less than two seconds so that the tests can be run on a very regular basis during development. As such, it might be useful to investigate the use of a tool like xdist and see whether or not it can run tests in parallel and improve performance.

[ilikerustoo]

It seems running xdist with pip works perfectly but does not run the tests when used with pipenv so far. I have tried on Travis CI, @Michionlion, and my own setup so far.

Also when running on pip here are my results while using xdist and not using it

============================= test session starts ==============================
platform linux -- Python 3.6.7, pytest-4.2.1, py-1.7.0, pluggy-0.8.1
rootdir: /home/mohammad/Documents/cs203/gatorgrouper, inifile: pytest.ini
plugins: xdist-1.26.1, forked-1.0.2
gw0 [23] / gw1 [23] / gw2 [23] / gw3 [23]
.......................                                                  [100%]
========================== 23 passed in 0.68 seconds ===========================

============================= test session starts ==============================
platform linux -- Python 3.6.7, pytest-4.2.1, py-1.7.0, pluggy-0.8.1
rootdir: /home/mohammad/Documents/cs203/gatorgrouper, inifile: pytest.ini
plugins: xdist-1.26.1, forked-1.0.2
collected 23 items                                                             

tests/test_absent.py ....                                                [ 17%]
tests/test_arguments.py .....                                            [ 39%]
tests/test_create_escaped_string.py ...                                  [ 52%]
tests/test_display.py .                                                  [ 56%]
tests/test_group_method.py ......                                        [ 82%]
tests/test_group_size.py ....                                            [100%]

========================== 23 passed in 0.16 seconds ===========================

It seems xdist has not sped up testing but there could be some extra configuration to correct this issue.