some more improvements after review.

[serjic]

1. returnType.GetTypeElement().IsDescendantOf()

var valueProperty = storage.BindToContextLive(lifetime, ContextRange.ApplicationWide)
.GetValueProperty();

    private static bool IsTestType(IDeclaredElement declaredElement)
    {
      var utm = declaredElement.GetSolution().GetComponent<IUnitTestElementStuff>();
      return declaredElement is ITypeElement && utm.IsElementOfKind(declaredElement, UnitTestElementKind.TestContainer);
    }

    private static bool IsTestMethod(IDeclaredElement declaredElement)
    {
      var utm = declaredElement.GetSolution().GetComponent<IUnitTestElementStuff>();
      return (declaredElement is IMethod || declaredElement is IProperty) && utm.IsElementOfKind(declaredElement, UnitTestElementKind.Test);
    }