I tried what you suggested.
//arrange
Isolate.Fake.StaticConstructor<SuperClassOfClassA>();
ClassA real = Isolate.Fake.Dependencies<ClassA>();
Isolate.NonPublic.WhenCalled(real, "method1").CallOriginal();
//act
Isolate.Invoke.Method(real, "method1", null);
//assert
Isolate.Verify.NonPublic.WasCalled(real, "method1");
But now, the point where I call the NonPublic method "method1" , I'm getting a null reference error.