RSpec - Unit Testing

1RSpec.describe OrderService do
2  describe '#process_order' do
3    let(:user) { create(:user) }
4    let(:product) { create(:product, price: 100) }
5    let(:order) { build(:order, user: user, items: [product]) }
6    let(:payment_gateway) { instance_double(PaymentGateway) }
7 
8    subject(:service) { described_class.new(payment_gateway) }
9 
10    before do
11      allow(payment_gateway).to receive(:charge).and_return(true)
12    end
13 
14    context 'when payment succeeds' do
15      it 'creates the order' do
16        expect { service.process_order(order) }
17          .to change(Order, :count).by(1)
18      end
19 
20      it 'charges the correct amount' do
21        service.process_order(order)
22        expect(payment_gateway).to have_received(:charge).with(100)
23      end
24    end
25 
26    context 'when payment fails' do
27      before do
28        allow(payment_gateway).to receive(:charge).and_raise(PaymentError)
29      end
30 
31      it 'raises an error' do
32        expect { service.process_order(order) }.to raise_error(PaymentError)
33      end
34    end
35  end
36end