Refactor create_item_adjustments_spec

To use in-memory items more.

core/spec/models/spree/promotion/actions/create_item_adjustments_spec.rb

@@ -4,11 +4,11 @@ module Spree
   class Promotion
     module Actions
       describe CreateItemAdjustments, type: :model do
-        let(:order) { create(:order) }
+        let(:order) { create(:order_with_line_items, line_items_count: 1) }
         let(:promotion) { create(:promotion, :with_line_item_adjustment, adjustment_rate: adjustment_amount) }
         let(:adjustment_amount) { 10 }
         let(:action) { promotion.actions.first! }
-        let!(:line_item) { create(:line_item, order: order) }
+        let(:line_item) { order.line_items.to_a.first }
         let(:payload) { { order: order, promotion: promotion } }
 
         before do
@@ -128,26 +128,32 @@ module Actions
           let(:promotion) { create(:promotion, :with_line_item_adjustment) }
           let(:other_promotion) { create(:promotion, :with_line_item_adjustment) }
 
-          it "destroys adjustments for incompleted orders" do
-            order = Order.create
-            action.adjustments.create!(label: "Check", amount: 0, order: order, adjustable: order)
+          context 'with incomplete orders' do
+            let(:order) { create(:order) }
 
-            expect {
-              action.destroy
-            }.to change { Adjustment.count }.by(-1)
+            it 'destroys adjustments' do
+              order.adjustments.create!(label: 'Check', amount: 0, order: order, source: action)
+
+              expect {
+                action.destroy
+              }.to change { Adjustment.count }.by(-1)
+            end
           end
 
-          it "nullifies adjustments for completed orders" do
-            order = Order.create(completed_at: Time.current)
-            adjustment = action.adjustments.create!(label: "Check", amount: 0, order: order, adjustable: order)
+          context 'with complete orders' do
+            let(:order) { create(:completed_order_with_totals) }
 
-            expect {
-              action.destroy
-            }.to change { adjustment.reload.source_id }.from(action.id).to nil
+            it 'nullifies adjustments for completed orders' do
+              adjustment = order.adjustments.create!(label: 'Check', amount: 0, order: order, source: action)
+
+              expect {
+                action.destroy
+              }.to change { adjustment.reload.source_id }.from(action.id).to nil
+            end
           end
 
           it "doesnt mess with unrelated adjustments" do
-            other_action.adjustments.create!(label: "Check", amount: 0, order: order, adjustable: order)
+            order.adjustments.create!(label: "Check", amount: 0, order: order, source: action)
 
             expect {
               action.destroy