Add support for running Pester tests

[rkeithhill]

I'm not exactly sure how to do this but I think it would be nice to have. Maybe this needs to wait for VSCode to have test-runner support (which may never happen)?

[daviwil]

I think @dfinke has done this before in VS Code. For now it just requires defining a task which can run Pester.

To take it further, we could implement our own Pester harness (possibly in PowerShell Editor Services) which could integrate with VS Code in a couple interesting ways:

• Use VS Code's text editor "decoration" support to add some highlighting or gutter icons to show which tests have passed or failed. One good example of doing this is Wallaby.js. Here are some API docs for text decorations.
• Use VS Code's "Code Lens" support to mark Pester methods with a "Run test" command so that we could invoke test methods directly. Here are some API docs on the Code Lens support. Code Lenses are being used in Visual Studio for stuff like this:

Could be an interesting feature to add!

[rkeithhill]

This has been partially addressed by PR #97, #98 and #105. However what we want is for VSCode to support creation of the tasks.json file with the Pester test task runner already configured in it rather than require the user to do that. See microsoft/vscode#2263

[TylerLeonhardt]

Looks like support for creation of the tasks.json file is supported. All that's left is to have the PowerShell extension create a test task that runs Pester.

[fourpastmidnight]

There's a great extension called Test Explorer UI, which is sort of a general "framework" for showing tests for a project. For each supported language, an adapter extension must be created, of which there currently are several: Jasmine Test Explorer, Mocha Test Explorer, .NET Core Test Explorer, just to name a few.

I had a brief thought to create such an adapter for Pester specifically (I can't remember the Pester issue I commented on about this very thing.)

[TylerLeonhardt]

@fourpastmidnight that would be awesome and would be a great addition to our ecosystem :)

Someone recently did something similar with Code Coverage https://www.pwsh.site/powershell/2019/01/10/how-to-enable-coverage-markings-in-vscode-for-your-powershell-projects.html

applying Pester to general purpose extensions.

It's a great idea!