Move promotion application spec to legacy_promotions

This spec is not feasible with the promotion system extracted within
core. Moving.

legacy_promotions/spec/requests/spree/api/promotion_application_spec.rb

@@ -0,0 +1,48 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe 'Promotion application', type: :request do
+  before do
+    stub_authentication!
+  end
+
+  context "with an available promotion" do
+    let!(:order) { create(:order_with_line_items, line_items_count: 1) }
+    let!(:promotion) do
+      promotion = create(:promotion, name: "10% off", code: "10off")
+      calculator = Spree::Calculator::FlatPercentItemTotal.create(preferred_flat_percent: "10")
+      action = Spree::Promotion::Actions::CreateItemAdjustments.create(calculator: calculator)
+      promotion.actions << action
+      promotion
+    end
+
+    it "can apply a coupon code to the order" do
+      expect(order.total).to eq(110.00)
+      post spree.api_order_coupon_codes_path(order), params: { coupon_code: "10off", order_token: order.guest_token }
+      expect(response.status).to eq(200)
+      expect(order.reload.total).to eq(109.00)
+      expect(json_response["success"]).to eq("The coupon code was successfully applied to your order.")
+      expect(json_response["error"]).to be_blank
+      expect(json_response["successful"]).to be true
+      expect(json_response["status_code"]).to eq("coupon_code_applied")
+    end
+
+    context "with an expired promotion" do
+      before do
+        promotion.starts_at = 2.weeks.ago
+        promotion.expires_at = 1.week.ago
+        promotion.save
+      end
+
+      it "fails to apply" do
+        post spree.api_order_coupon_codes_path(order), params: { coupon_code: "10off", order_token: order.guest_token }
+        expect(response.status).to eq(422)
+        expect(json_response["success"]).to be_blank
+        expect(json_response["error"]).to eq("The coupon code is expired")
+        expect(json_response["successful"]).to be false
+        expect(json_response["status_code"]).to eq("coupon_code_expired")
+      end
+    end
+  end
+end