Test Studio supports adding a single custom base test class in the project. If one more base test class is defined and listed in a test code-behind file, the coded steps will be listed as empty and will not show the option to choose any of the methods in the test class.The steps will be still executed, but no changes can be applied within Test Studio (only in VS).

because I want many test sharing the same OnAfterTestCompleted(), instead of adding it to each test, I created new class:

using....

namespace test_studio_tests
{
    public class CustomWebAiiTest : BaseWebAiiTest
    {
        public override void OnAfterTestCompleted(TestResult result)
        {
            // some code to be executed 
        }
    }
}

and then all the tests to inherit from this new class

public class TestClass : CustomWebAiiTest

instead of Base one as they did so far. in TS project keep compiling, but then all the tests have extra icon and coded steps are not recognized anymore. in the meantime in VS2022 with TS plugin, all is recognized and keep working without any issue.