test: update ResizeMixin tests to use nextResize helper

packages/component-base/test/resize-mixin.test.js

@@ -4,6 +4,15 @@ import sinon from 'sinon';
 import { html, PolymerElement } from '@polymer/polymer/polymer-element.js';
 import { ResizeMixin } from '../src/resize-mixin.js';
 
+const nextResize = (target) => {
+  return new Promise((resolve) => {
+    new ResizeObserver((_, observer) => {
+      observer.disconnect();
+      setTimeout(resolve);
+    }).observe(target);
+  });
+};
+
 describe('resize-mixin', () => {
   let element, observeParent;
 
@@ -25,29 +34,21 @@ describe('resize-mixin', () => {
         get _observeParent() {
           return observeParent;
         }
-
-        _onResize() {
-          this.__resolveResize?.();
-        }
-
-        nextResize() {
-          return new Promise((resolve) => {
-            this.__resolveResize = resolve;
-          });
-        }
       },
     );
   });
 
   beforeEach(async () => {
     element = fixtureSync(`<resize-mixin-element></resize-mixin-element>`);
     // Wait for the initial resize.
-    await element.nextResize();
+    await nextResize(element);
   });
 
   it('should notify resize', async () => {
+    const spy = sinon.spy(element, '_onResize');
     element.style.width = '100px';
-    await element.nextResize();
+    await nextResize(element);
+    expect(spy.calledOnce).to.be.true;
   });
 
   it('should not notify resize for detached element', async () => {
@@ -86,12 +87,14 @@ describe('resize-mixin', () => {
       beforeEach(async () => {
         parent.appendChild(element);
         // Wait for the initial resize.
-        await element.nextResize();
+        await nextResize(parent);
       });
 
       it('should notify parent element resize', async () => {
+        const spy = sinon.spy(element, '_onResize');
         parent.style.width = '100px';
-        await element.nextResize();
+        await nextResize(parent);
+        expect(spy.calledOnce).to.be.true;
       });
 
       describe('multiple children', () => {
@@ -131,12 +134,14 @@ describe('resize-mixin', () => {
         parent.attachShadow({ mode: 'open' });
         parent.shadowRoot.appendChild(element);
         // Wait for the initial resize.
-        await element.nextResize();
+        await nextResize(parent);
       });
 
       it('should notify shadow host resize', async () => {
+        const spy = sinon.spy(element, '_onResize');
         parent.style.width = '100px';
-        await element.nextResize();
+        await nextResize(parent);
+        expect(spy.calledOnce).to.be.true;
       });
     });
   });