Unit test fails when use try/catch

Question

I need to test that exactly Argument Exception is caugtht. Is it really possible to understand that exception in method is caugtht?

    public JsonResult Create(TeamViewModel teamViewModel)
    {
        JsonResult result = null;
            try
            {
                // here exception throws
                var domainTeam = teamViewModel.ToDomain();
                  ...
            }
            catch (ArgumentException ex)
            {
                this.ModelState.AddModelError(string.Empty, ex.Message);
                result = this.Json(this.ModelState);
            }           

        return result;
    }

My Unit test for this method:

 public void Create_InvalidTeamAchievements_ArgumentExceptionThrown()
 {
    Exception exception = null;
    string invalidAchievements = CreateInvalidTeamAchievements();

    // Arrange
    var viewModel = new TeamMvcViewModelBuilder().WithAchievements(invalidAchievements).Build();
    var sut = _kernel.Get<TeamsController>();

    // Act
    try
    {
        sut.Create(viewModel);
    }
    catch (ArgumentException ex)
    {
        exception = ex;
    }

    // Assert
    VerifyExceptionThrown(exception, string.Format(Resources.ValidationTeamAchievements, 
                Constants.Team.MAX_ACHIEVEMENTS_LENGTH));
}

Answer 1

You are testing it in wrong way. Functionality should be tested to not throw exception as you already have caught exception inside Create Method. Rather you should Assert that JsonResult containing your ModelState should have error in it in case exception was raised in Create method.