If there are more that one mock objects existing in the test, Mock.Assert wrongly succeeds while evaluating arrangements for each mock, but not the very first one. This is a regression compared to an older version from 2012. The following sample demonstrates the case: public interface IFoo { void Bar(); } [TestClass] public class UnitTest1 { [TestMethod] public void TestMethod1() { var bar = Mock.Create<IFoo>(); Mock.Arrange(() => bar.Bar()).OccursOnce(); var foo = Mock.Create<IFoo>(); Mock.Arrange(() => foo.Bar()).OccursOnce(); Mock.Assert(foo); // Would wrongly succeed Mock.Assert(bar); // Would fail as expected } }