public async Task RegisterTaskReturnsJsonWhenThereIsModelStateError() { const string modelStateErrorMessage = "modelStateErrorMessage"; var sut = new TaskApiController(null, null, null); sut.AddModelStateErrorWithErrorMessage(modelStateErrorMessage); var jsonResult = await sut.RegisterTask(new ActivitySignupViewModel()) as JsonResult; var result = jsonResult.GetValueForProperty <List <string> >("errors"); Assert.IsType <JsonResult>(jsonResult); Assert.IsType <List <string> >(result); Assert.Equal(result.First(), modelStateErrorMessage); }