如何使用 Rspec 测试控制器中的销毁故障？

Question

I have a books controller with the following action...

def destroy
   @book = Book.find(params[:id])
   if @book.destroy
     redirect_to(books_path)
   else
     render('delete')
   end
 end

I am able to test the the first if case, but not the situation where @book.destroy returns false. My question is - how do I make @book.destroy fail? I want to write a rspec test to cover that case.

describe "destroy" do
   before(:context) do
     @book = create(:book)
   end
   context "failing the destroy function" do
     it "renders delete" do
       allow(@book).to receive(:destroy).and_return(false)
       delete :destroy, params: { id: @book.id }
       expect(response).to render_template(:delete)
     end
   end
 end

I tried writing the above thinking that allow(@book).to receive(:destroy).and_return(true) would make destroy() return false, but instead, it still returns true and tests the code in the first if statement. I have no idea how to cover the code in the else statement. Any help please?

Thanks.

Answer 1

The main reason your test does not work is that Book.find will load the record from the database and create a new instance of the class which means that #destroy is not being called on the same object that you have stubbed.

You need to stub the Book.find method so that it returns the book instance with the stubbed method:

describe "destroy" do
  context "failing the destroy function" do
    let(:book) { build_stubbed(:book) } # use let instead of ivars

    # don't use before :context unless you actually 
    # have a real reason. You should strive to have 
    # each example setup/teardown on their own 
    before do
      allow(book).to receive(:destroy).and_return(false)
      allow(Book).to receive(:find).and_return(book)
    end 

    it "renders delete" do
      delete :destroy, params: { id: book.id }
      expect(response).to render_template(:delete)
    end
  end
end