Following your guide about Unit Testing I was able to generate a unit test project (PHP Console project).
I've added this as a new project to a solution with multiple other PHP and C# projects as well as other C# Unit Test projects.
Unfortunately the VS Test Explorer only recognizes the C# Unit Test projects but shows no tests from the PHP Unit Test project.
I've then created a blank VS Solution file and added my existing PHP Unit Test project to the new blank VS Solution.
To my surprise, in this Solution the VS Test Explorer correctly recognizes my PHP Unit Tests.
So my assumption would be that it is not possible to have PHP Unit Tests in a solution with other non-PHP Unit Tests and/or other non-PHP projects.
Could you please give me a hint whether I'm making something wrong here?