V4: Allow for arbitrary test group nesting

[dlwyatt]

Describe / Context become basically aliases for the same command, ideally. Allow any combination of Describe / Context that a test author wants to provide.

This will involve breaking changes to both NUnit XML output and PassThru. (Instead of an array of TestResult objects, we'll likely wind up with a hierarchy of TestGroup / TestResult objects very similar to the structure of NUnit XML.)

The test scripts themselves should also be promoted to first-class citizens, if possible. That way Describe / Context are optional (it'll be valid to just have test cases in a file, if desired), and more importantly we can do BeforeAll / AfterAll blocks that apply to an entire file. (Not sure how easy this will be for Gherkin scenarios; needs investigation.)

Note: Big concern here is functionality of -Tag and -ExcludeTag. Right now they only work on the outermost test groups (Describe). In the new setup, tags will be applicable at any level, because Describes are nestable. Right now, Pester's logic would be pretty stupid about Tag / ExcludeTag. What we'd need is to analyze the structure of the test script ahead of time and come up with a plan for which test groups to run. There are some good ideas on this topic with @redoz on Twitter: https://twitter.com/redoz/status/737728099350106113

[dlwyatt]

This has been partially implemented. Still need to figure out how to handle tags in nested test groups, update the -PassThru object, and write lots of new documentation / tests.

[it-praktyk]

@dlwyatt, can you provide an update? Yeah, I didn't read the code for this.

[nohwnd]

Test groups can be nested now, and the result object is hierarchical. Making tests run outside of Describe, and still be able to do all the "infrastructure" setup, and handle teardowns and setups is difficult. Similarly placing After* blocks outiside of describe is problematic in interactive mode, because you don't know which describe is the last on and you cannot rely on AfterAll to be placed at the end.

Right now v5 adds one more block above the Describe to handle multiple describes in the same file, and does not support interactive mode. If the interactive mode is implemented as running the saved file from the code then it would all work well.

I am not sure what about plain unsaved code, and how to run it without being in a file. What is already possible is doing Invoke-Pester -ScriptBlock, so probably something like that.

Overall allowing It blocks ouside of Describe is a lot of work that is not worth it.

Tracking the interactive mode here #1268

The filtering on block or test level works