public void BeCalledWhenInvoked() { // Arrange var mockedSet = new Mock <DbSet <ICreature> >(); var mockedDbContext = new Mock <IAquaWorldDbContext>(); mockedDbContext.Setup(x => x.Set <ICreature>()).Returns(mockedSet.Object); var dataProvider = new EfAquaWorldDataProvider <ICreature>(mockedDbContext.Object); var mockedAdvert = new Mock <ICreature>(); // Act try { dataProvider.Detach(mockedAdvert.Object); } catch (NullReferenceException) { }; // Assert mockedDbContext.Verify(x => x.Entry(mockedAdvert.Object), Times.AtLeastOnce); }