public void ClearTest() { IExtensibleMapper <TSource, TTarget> mapper = new ManualMapper <TSource, TTarget>(); var target = new MappingRepository(); target.AddMapper(mapper); target.Clear(); var mappersField = target.GetType().GetField("mappers", BindingFlags.NonPublic | BindingFlags.Instance); var mappers = (IEnumerable)mappersField.GetValue(target); Assert.IsFalse(mappers.Cast <object>().Any()); }