Update TESTGUIDE.md (#17663)

Author: psfinaki

TESTGUIDE.md

@@ -114,7 +114,7 @@ The F# tests are split as follows:
 
 ### FSharp Suite
 
-This is compiled using [tests\fsharp\FSharp.Tests.FSharpSuite.fsproj](tests/fsharp/FSharp.Tests.FSharpSuite.fsproj) to a unit test DLL which acts as a driver script. Each individual test is an NUnit test case, and so you can run it like any other NUnit test.
+This is compiled using [tests\fsharp\FSharp.Tests.FSharpSuite.fsproj](tests/fsharp/FSharp.Tests.FSharpSuite.fsproj) to a unit test DLL which acts as a driver script. Each individual test is an xUnit test case, and so you can run it like any other xUnit test.
 
 ```shell
 .\build.cmd net40 test-net40-fsharp
@@ -151,9 +151,9 @@ Tags are in the left column, paths to to corresponding test folders are in the r
 
 If you want to re-run a particular test area, the easiest way to do so is to set a temporary tag for that area in test.lst (e.g. "RERUN") and adjust `ttags` [run.fsharpqa.test.fsx script](tests/fsharpqa/run.fsharpqa.test.fsx) and run it.
 
-### VisualFSharp.UnitTests, FSharpSuite.Tests
+### VisualFSharp.UnitTests
 
-These are all currently NUnit tests (we hope to migrate them to xUnit). You can execute these tests individually via the Visual Studio NUnit3 runner
+These are currently NUnit tests (we hope to migrate them to xUnit). You can execute these tests individually via the Visual Studio NUnit3 runner
 extension or the command line via `nunit3-console.exe`.
 
 Note that for compatibility reasons, the IDE unit tests should be run in a 32-bit process,