New article that details unit test code coverage using coverlet

[IEvangelist]

Summary

Adding new article that details unit test code coverage using coverlet.

• Adjust next steps in existing article
• Add "code coverage" section to best practices
• New articles detailing coverlet and dotnet test --collect:"Data Collector"
• Update ToC

Fixes #1477, and fixes #17255

Preview

✔️     NEW: Use code coverage for unit testing
✔️     UPDATE: Unit testing best practices with .NET Core and .NET Standard

[tdykstra]

This looks great, I just had some suggestions to change wording here and there, include some guidance on choosing among alternatives, and include some output examples.

[IEvangelist]

Ping @tdykstra and @BillWagner - I flipped this back over to "ready for review". I've made huge updates to it, since it was approved from Tom initially.

[tdykstra]

I'll take another look this afternoon.

[tdykstra]

Given the tutorial format, I wonder if a further structural change would be useful -- right now the directions have them doing 2 unit test projects and include partial instructions for a 3rd. As a tutorial, it might work better as 3 , that is, up front give the three options and tell how to choose, then have a separate sequence of instructions for each choice. That way they get to follow instructions fully covering their chosen approach while not having to do steps that pertain to an approach that is irrelevant for them.

[tdykstra]

Does this method of including line breaks work equally well in PowerShell, CMD, on Linux, and on macOS? If not it might be better to create a separate block for each command.

[IEvangelist]

There are no line breaks, just && and cd commands. Both of which are cross platform.