public async Task RegisterEventReturnsCorrectJsonWhenModelStateIsNotValid() { const string modelStateErrorMessage = "modelStateErrorMessage"; var sut = new EventApiController(null); sut.AddModelStateErrorWithErrorMessage(modelStateErrorMessage); var jsonResult = (JsonResult)await sut.RegisterEvent(new EventSignupViewModel()); var result = jsonResult.GetValueForProperty <List <string> >("errors"); Assert.IsType <JsonResult>(jsonResult); Assert.IsType <List <string> >(result); Assert.Equal(result.First(), modelStateErrorMessage); }