Save this snippet in:

%USERPROFILE%\Documents\Visual Studio 2020\Code Snippets\Visual C#\My Code Snippets\

Name your snippet something like unittest.snippet.

In Visual Studio, you will then just type ut and hit tab twice to use this snippet.

If you have Resharper installed, you will either need to switch back to Visual Studio Intellisense in Resharper's options or use Ctrl+K, X to bring up the snippet menu.