Improve spec for Spree::Order#finalize!

spec/models/spree/order_spec.rb

@@ -216,35 +216,36 @@
     end
   end
 
-  context "#finalize!" do
-    let(:order) { Spree::Order.create }
+  describe "#finalize!" do
+    subject(:order) { Spree::Order.create }
+
     it "should set completed_at" do
-      expect(order).to receive(:touch).with(:completed_at)
-      order.finalize!
+      expect {
+        order.finalize!
+        order.reload
+      }.to change {
+        order.completed_at
+      }.from(nil)
     end
 
-    it "should sell inventory units" do
-      order.shipments.each do |shipment|
-        expect(shipment).to receive(:update!)
-        expect(shipment).to receive(:finalize!)
-      end
-      order.finalize!
-    end
+    it "updates shipments and decreases stock" do
+      order = create(:order_ready_for_confirmation)
+      shipment = order.shipments.first
+      shipment.update_columns(updated_at: 1.minute.ago)
 
-    it "should decrease the stock for each variant in the shipment" do
-      order.shipments.each do |shipment|
-        expect(shipment.stock_location).to receive(:decrease_stock_for_variant)
-      end
-      order.finalize!
+      expect {
+        order.finalize!
+      }.to change { order.variants.first.on_hand }.by(-1)
+        .and change { shipment.updated_at }
     end
 
     it "should change the shipment state to ready if order is paid" do
-      Spree::Shipment.create(order:)
-      order.shipments.reload
+      order = create(:order_ready_for_confirmation)
 
-      allow(order).to receive_messages(paid?: true, complete?: true)
-      order.finalize!
+      order.payments.first.capture!
+      order.next! # calls `finalize!`
       order.reload # reload so we're sure the changes are persisted
+
       expect(order.shipment_state).to eq 'ready'
     end