Add pending integration spec for orders adjustments page

None of this works right now, but let's write a spec that details how
things should work.

promotions/spec/system/solidus_promotions/backend/orders/adjustments_spec.rb

@@ -0,0 +1,87 @@
+# frozen_string_literal: true
+
+require "rails_helper"
+
+RSpec.describe "Adjustments", :pending, type: :feature do
+  stub_authorization!
+
+  let!(:ship_address) { create(:address) }
+  let!(:tax_zone) { create(:global_zone) } # will include the above address
+  let!(:tax_rate) { create(:tax_rate, name: "Sales Tax", amount: 0.20, zone: tax_zone, tax_categories: [tax_category]) }
+
+  let!(:line_item) { order.line_items[0] }
+
+  let(:tax_category) { create(:tax_category) }
+  let(:variant) { create(:variant, tax_category:) }
+
+  before(:each) do
+    order.recalculate
+
+    visit spree.admin_path
+    click_link "Orders"
+    uncheck "Only show complete orders"
+    click_button "Filter Results"
+    within_row(1) { click_icon :edit }
+    click_link "Adjustments"
+  end
+
+  let!(:order) { create(:order, line_items_attributes: [{ price: 10, variant: }]) }
+
+  context "when the order is completed" do
+    let!(:order) do
+      create(
+        :completed_order_with_totals,
+        line_items_attributes: [{ price: 10, variant: }],
+        ship_address:
+      )
+    end
+
+    let!(:adjustment) { order.adjustments.create!(order:, label: "Rebate", amount: 10) }
+
+    it "shows adjustments" do
+      expect(page).to have_content("Adjustments")
+    end
+
+    context "when the promotion system is configured to allow applying promotions to completed orders" do
+      before do
+        expect(SolidusPromotions.config).to receive(:recalculate_complete_orders).and_return(true)
+      end
+
+      it "shows input field for promotion code" do
+        expect(page).to have_content("Adjustments")
+        expect(page).to have_field("coupon_code")
+      end
+    end
+
+    context "when the promotion system is configured to not allow applying promotions to completed orders" do
+      before do
+        expect(SolidusPromotions.config).to receive(:recalculate_complete_orders).and_return(false)
+      end
+
+      it "does not show input field for promotion code" do
+        expect(page).to have_content("Adjustments")
+        expect(page).not_to have_field("coupon_code")
+      end
+    end
+  end
+
+  it "shows the input field for applying a promotion" do
+    expect(page).to have_field("coupon_code")
+  end
+
+  context "creating a manual adjustment" do
+    let!(:adjustment_reason) { create(:adjustment_reason, name: "Friendly customer") }
+    before do
+      click_link "New Adjustment"
+    end
+
+    it "creates a new adjustment" do
+      fill_in "adjustment_amount", with: "5"
+      fill_in "adjustment_label", with: "Test Adjustment"
+      select "Friendly customer", from: "Reason"
+      click_button "Continue"
+      expect(page).to have_content("Adjustment has been successfully created!")
+      expect(page).to have_content("Test Adjustment")
+    end
+  end
+end