Example showing discovery and running of test commands

[vyadh]

I couldn't use nupm as it was marked as experimental so I thought I'd see how far I could take the "reflection" capabilities of Nushell for basic unit testing. I imagine we could create a somewhat full-featured test framework using something like this technique. I'm somewhat tempted to try 😄.

I can simplify the example by removing the ignored tests and printing of test names if you prefer, but it seemed useful enough to leave in.

[vyadh]

Minor update to comply with #1601 and test compatibility with nupm, which I now realise works in a similar way. Maybe there is some appetite to update nupm to allow the test runner to also work for non-module tests. The use case being what I often do, which is write various test scripts in Nushell, but the implementation might be something else - such as testing infrastructure or even bash scripts.

[fdncred]

Thanks