how to test for the responses of a method using NUnit test

Question

i'm new to unit test in c#, i want to test for the 3 possible outcome, when modalstate is invalid, adding new category and internal server error. here is the method i want to test.

        [HttpPost]
        public async Task<ActionResult<Category>> CreateCategory(CreateCategoryDTO createCategoryDto)
        {
            if (!ModelState.IsValid)
            {
                _logger.LogError($"Invalid POST attempt in {nameof(CreateCategory)}");
                return BadRequest(new Response{ Status = "fail", Message = "Invalid inputs"});
            }

            try
            {
                var category = _mapper.Map<Category>(createCategoryDto);
                await _unitOfWork.Categories.Add(category);
                await _unitOfWork.Save();
                return CreatedAtRoute("GetCategory", new {id = category.Id}, category);
            }
            catch (Exception e)
            {
                _logger.LogError($"Something went wrong in the {nameof(CreateCategory)}");
                return StatusCode(500, "Internal server error. Please try again later");
            }
        }

and here is my code so far, please does anyone know how i can access the 3 possible responses?

    [SetUp]
    public void Setup()
    {
        _categories = new Mock<IRepository<Category>>();
        _unitOfWork = new Mock<IUnitOfWork>();
        _unitOfWork.SetupGet(work => work.Categories).Returns(_categories.Object);
        _logger = new Mock<ILogger<CategoryController>>();
        _mapper = new Mock<IMapper>();
        _categoryController = new CategoryController(_logger.Object, _mapper.Object,_unitOfWork.Object);
    }

    [Test]
    public void CreateCategoryTest()
    {
        _categoryController.ModelState.AddModelError("test", "test");
        var result = _categoryController.CreateCategory(new CreateCategoryDTO()).GetAwaiter().GetResult();
        
    }

Answer 1

It is not unit testing. If you test Controller it's about integration testing. Ok. If you want 3 test case, you should write 3 test. Because one test is one test case. Don't try test it in one place