public void Delete() { //Arrange var idForRemove = 1; _mock.Setup(s => s.Delete(It.IsAny <int>())).Returns <int>(id => { var removeExercise = _exercises.Find(ex => ex.Id == id); _exercises.Remove(removeExercise); return(new OperationResult { Succeed = true, ResultItemId = id }); }); //Act var result = _exerciseController.Delete(idForRemove); var operationResult = result as OkNegotiatedContentResult <IOperationResult>; //Assert Assert.IsInstanceOfType(result, typeof(OkNegotiatedContentResult <IOperationResult>)); Assert.IsTrue(operationResult.Content.Succeed); Assert.IsTrue(operationResult.Content.ResultItemId > 0); Assert.IsFalse(_exercises.Any(ex => ex.Id == operationResult.Content.ResultItemId)); }