PortfolioControllerTests.cs

[HttpGet]
public async Task<IActionResult> Detail(int id)
{
    if (id == default(int)) return BadRequest();

    var model = await _mediator.Send(new PortfolioByIdQuery { PortfolioId = id });

    if (model == null) return NotFound();

    var viewModel = _mapper.Map<Portfolio, PortfolioViewModel>(model);

    return View(viewModel);
}