test: address review feedback on drag-and-drop regression tests

- DropZoneSpec: spy on the real Event.prototype.stopPropagation
  instead of relying only on document-level bubbling, since
  MockDragEvent's own stopPropagation is never actually invoked by
  fireEvent (it only reads known DragEvent init properties)
- DmnEditorPage#dragRule: wait for the handle/row and fail with a
  clear error instead of crashing on a null boundingBox()
- dmn-modeling.spec: assert both rule ids are present in the saved
  XML before comparing their positions, so a missing rule can't
  produce a false pass

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: barmac

client/src/app/drop-zone/__tests__/DropZoneSpec.js

@@ -165,11 +165,18 @@ describe('<DropZone>', function() {
       // `document`; this drop zone wraps that tree and must let such events
       // bubble on past it rather than swallowing them
       // (https://github.com/camunda/camunda-modeler/issues/6166)
+      //
+      // `fireEvent.drop` builds a real native DragEvent from `MockDragEvent`
+      // (used only as a property bag — its own no-op `stopPropagation` is
+      // never actually invoked), so this spies on the real `Event.prototype`
+      // method rather than on the mock, and independently confirms the event
+      // still reaches a `document`-level listener, i.e. it truly bubbles
 
       // given — a listener above the zone's own React root, mirroring where
       // dmn-js's own drag-and-drop handling lives in the real app
       const { dropzone } = renderDropZone();
 
+      const stopPropagationSpy = sinon.spy(window.Event.prototype, 'stopPropagation');
       const outerDropSpy = sinon.spy();
 
       document.addEventListener('drop', outerDropSpy);
@@ -180,9 +187,11 @@ describe('<DropZone>', function() {
         fireEvent.drop(dropzone, new MockDragEvent());
 
         // then
+        expect(stopPropagationSpy).to.have.not.been.called;
         expect(outerDropSpy).to.have.been.calledOnce;
       } finally {
         document.removeEventListener('drop', outerDropSpy);
+        stopPropagationSpy.restore();
       }
 
     });

test/e2e/pages/DmnEditorPage.js

@@ -130,9 +130,20 @@ class DmnEditorPage extends DiagramEditorPage {
     const handle = this.page.locator(`[data-row-id="${ ruleId }"] .dmn-icon-drag.vertical`);
     const targetRow = this.page.locator(`[data-row-id="${ targetRuleId }"]`).first();
 
+    await handle.waitFor();
+    await targetRow.waitFor();
+
     const handleBox = await handle.boundingBox();
     const targetBox = await targetRow.boundingBox();
 
+    if (!handleBox) {
+      throw new Error(`could not determine the drag handle position for rule "${ ruleId }"`);
+    }
+
+    if (!targetBox) {
+      throw new Error(`could not determine the row position for rule "${ targetRuleId }"`);
+    }
+
     const startX = handleBox.x + handleBox.width / 2;
     const startY = handleBox.y + handleBox.height / 2;
 

test/e2e/specs/dmn-modeling.spec.js

@@ -360,7 +360,12 @@ test.describe('DMN modeling', function() {
 
       const xml = await readFile(output);
 
-      expect(xml.indexOf('id="Rule_2"')).toBeLessThan(xml.indexOf('id="Rule_1"'));
+      const rule1Index = xml.indexOf('id="Rule_1"');
+      const rule2Index = xml.indexOf('id="Rule_2"');
+
+      expect(rule1Index).toBeGreaterThan(-1);
+      expect(rule2Index).toBeGreaterThan(-1);
+      expect(rule2Index).toBeLessThan(rule1Index);
     });
   });