Add specs for customers_dot proxy

app/controllers/customers_dot/proxy_controller.rb

@@ -5,6 +5,8 @@ module CustomersDot
     skip_before_action :authenticate_user!
     skip_before_action :verify_authenticity_token
 
+    feature_category :purchase
+
     BASE_URL = Gitlab::SubscriptionPortal::SUBSCRIPTIONS_URL
 
     def graphql

spec/controllers/customers_dot/proxy_controller_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe CustomersDot::ProxyController do
+  describe 'POST graphql' do
+    let_it_be(:customers_dot) { "#{Gitlab::SubscriptionPortal::SUBSCRIPTIONS_URL}/graphql" }
+
+    it 'forwards request body to customers dot' do
+      request_body = '{ "foo" => "bar" }'
+
+      stub_request(:post, customers_dot)
+
+      post :graphql, body: request_body
+
+      expect(WebMock).to have_requested(:post, customers_dot).with(body: request_body)
+    end
+
+    it 'responds with customers dot status' do
+      stub_request(:post, customers_dot).to_return(status: 500)
+
+      post :graphql
+
+      expect(response).to have_gitlab_http_status(:internal_server_error)
+    end
+
+    it 'responds with customers dot response body' do
+      customers_dot_response = 'foo'
+
+      stub_request(:post, customers_dot).to_return(body: customers_dot_response)
+
+      post :graphql
+
+      expect(response.body).to eq(customers_dot_response)
+    end
+  end
+end