Python unit testing

[PDoakORNL]

If we are going to generate important results with python we should consider (must in my opinion) python unit test.
I've used python's built in unittest in the past.

[markdewing]

I prefer the syntax of pytest, but there is a definite advantage to using a built-in facility.

[PDoakORNL]

I'll take a look at it. I don't think unittest is optimal its just the one I've used.

[jtkrogel]

N.B. Nexus related tests take a slightly different philosophy. The tests there (see https://github.com/QMCPACK/qmcpack/blob/develop/nexus/bin/nxs-test) are most fairly termed integration tests as they do not contain mock classes, however, once complete, the tests will be called in bottom up dependency order which has a similar effect to unit tests plus mocks. I have no firm opinion about Python tests outside Nexus.

[fdmalone]

The afqmctools use unittest. However, they aren't currently running automatically anywhere.

[jtkrogel]

N.B. A subset of Nexus tests can now be run with pytest or nose. This subset is likely to expand in the future, but all tests will remain runnable via nxs-test without reliance on either pytest or nose.