public void Create() { // Arrange var countTrainings = _trainings.Count; var newTraining = new Training { MainTrainingPurpose = "The main purpose is 4...", Description = "Desc 4", StartDateTime = DateTime.Now, EndDateTime = DateTime.Now.AddHours(1).AddMinutes(40), }; _mock.Setup(s => s.Create(It.IsAny <TrainingDTO>())).Returns <TrainingDTO>(newItem => { newItem.Id = _trainings.Count + 1; newItem.CreatedDate = DateTime.Now; newItem.ModifiedDate = DateTime.Now; _trainings.Add(newItem); return(new OperationResult { ResultItemId = newItem.Id, Succeed = true }); }); // Act var result = _trainingController.Create(newTraining); var operationResult = result as OkNegotiatedContentResult <IOperationResult>; // Assert Assert.IsInstanceOfType(result, typeof(OkNegotiatedContentResult <IOperationResult>)); Assert.AreEqual(countTrainings + 1, _trainings.Count); Assert.IsTrue(operationResult.Content.Succeed); Assert.IsTrue(operationResult.Content.ResultItemId > 0); }