Built tests are not added to the Visual Studio Test Explorer window

I experience this same problem, but the solution was different.

Following the advice on a SpecFlow Github issue, the following worked for me:

1. Close all Visual Studio instances
2. Go to %TEMP%\VisualStudioTestExplorerExtensions\
3. Delete all the folders in here
4. Try again

in order to configure it to generate MSTest tests you need to add this to your app.config:

<specFlow>    
  <unitTestProvider name="MSTest"></unitTestProvider>
</specFlow>

if the tests are not showing in the test explorer you need to install NUnit test adapter :

go to Tools->Extensions and updates ->Online->Visual Studio Gallery->Tools->Testing and select NUnit Test Adapter

Visual Studio can change the default processor architecture when it loads. While looking endlessly trying to figure out the issue, I finally figured it out, that it wasn't really Specflow causing the issue.

If you have references that require a special architecture, it will prevent the tests from showing up in the test explorer. Change the architecture to x86 or x64 based on your needs.

Another thing you can do to see the build issues is open the Output window and change the dropdown to Tests during build. It will highlight any information of things taking place during your build.

I felt somebody should mention it just in case.