ruby - How to test exception raising in Rails/RSpec?

Question

There is the following code:

def index
    @car_types = car_brand.car_types
end

def car_brand
    CarBrand.find(params[:car_brand_id])
    rescue ActiveRecord::RecordNotFound
        raise Errors::CarBrandNotFound.new 
end

I want to test it through RSpec. My code is:

it 'raises CarBrandNotFound exception' do
    get :index, car_brand_id: 0
    expect(response).to raise_error(Errors::CarBrandNotFound)
end

CarBrand with id equaling 0 doesn't exist, therefore my controller code raises Errors::CarBrandNotFound, but my test code tells me that nothing was raised. How can I fix it? What do I wrong?

Answer 1

In order to spec error handling, your expectations need to be set on a block; evaluating an object cannot raise an error.

So you want to do something like this:

expect {
  get :index, car_brand_id: 0
}.to raise_error(Errors::CarBrandNotFound)

See Expect error for details.

I am a bit surprised that you don't get any exception bubbling up to your spec results, though.