Live Unit Testing .NET Core - Where are my tests?

So you're sitting in front of your computer, wondering why your unit tests won't show up in Visual Studio's Live Test Window. They appear fine in the normal Tests Window and they run without problems, you haven't done anything weird and all you want is to be able to see whether your code works.

You're not alone and there is a solution!

Background

Visual Studio has an awesome feature called "Live Unit Testing" which allows you to see whether your code passes automated tests. It will keep track of which tests affect each line of your code and run them when that code changes - giving you (close to) real-time feedback on the quality of your code.

It works brilliantly, but here are certain situations in which it just fails to pick up your tests altogether.

Where are my tests?

Microsoft.NET.Test.Sdk

It turns out this library is actually a hard requirement for your tests to appear in Live Unit Testing. Without it you'll see the following error in the Live Unit Testing output window.

Exception filtering tests: No tests matched the filter because it contains one or more properties that are not valid (TestCategory, Category). Specify filter expression containing valid properties (DisplayName, FullyQualifiedName) and try again.

To fix this issue, simply add the following package reference to your test project.

<PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.3.0" />

Restoring your packages with dotnet restore should then result in your tests appearing and running automatically.

Closing

Why this isn't immediately obvious to the user and why the exception message is completely opaque is beyond me, however this is a quick fix and should help get you back on track.

Have fun and go squash some bugs!