Hi Neil,
You need to clean up the fakes between the verifications.
This should work:
[Test]
public void Test()
{
A a = Isolate.Fake.Instance<A>(Members.CallOriginal);
a.Method();
Isolate.Verify.NonPublic.WasCalled(a, "PrivateMethod");
Isolate.CleanUp();
a.Method();
Isolate.Verify.NonPublic.WasNotCalled(a, "PrivateMethod");
}
Please let me know if it helps.