Given:
public interface IA { void TestMethod(); } public interface IB : IA { }
Why:
typeof(IB).GetMethods().Count() ==
You have to define some Bindingflags into GetMethods().
Try
typeof(IB).GetMethods(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.FlattenHierarchy).Count();