add tests for onScrolledToBottom

Author: iAmNathanJ

polaris-react/src/components/Scrollable/tests/Scrollable.test.tsx

@@ -3,6 +3,7 @@ import {mountWithApp} from 'tests/utilities';
 
 import {Scrollable} from '../Scrollable';
 import {ScrollableContext} from '../context';
+import type {ScrollableProps} from '../Scrollable';
 
 describe('<Scrollable />', () => {
   it('mounts', () => {
@@ -71,4 +72,60 @@ describe('<Scrollable />', () => {
       tabIndex: 0,
     });
   });
+
+  it('calls onScrolledToBottom when scrolled to bottom', () => {
+    const onScrolledToBottom = jest.fn();
+
+    const scrollArea = mountWithApp(
+      <Scrollable
+        data-test-id="scroll-element"
+        onScrolledToBottom={onScrolledToBottom}
+      >
+        <p>Hello</p>
+      </Scrollable>,
+    );
+
+    const scrollNode = scrollArea.find('div', {
+      'data-test-id': 'scroll-element',
+    } as ScrollableProps)?.domNode!;
+
+    // defineProperty needed to assign values to readonly node properties
+    Object.defineProperty(scrollNode, 'clientHeight', {get: () => 0});
+    Object.defineProperty(scrollNode, 'scrollHeight', {get: () => 10});
+    Object.defineProperty(scrollNode, 'scrollTop', {get: () => 10});
+
+    scrollArea.act(() => {
+      scrollNode.dispatchEvent(new Event('scroll'));
+    });
+
+    expect(onScrolledToBottom).toHaveBeenCalledTimes(1);
+  });
+
+  it(`doesn't call onScrolledToBottom when the scroll area is not overflowing`, () => {
+    const onScrolledToBottom = jest.fn();
+
+    const scrollArea = mountWithApp(
+      <Scrollable
+        data-test-id="scroll-element"
+        onScrolledToBottom={onScrolledToBottom}
+      >
+        <p>Hello</p>
+      </Scrollable>,
+    );
+
+    const scrollNode = scrollArea.find('div', {
+      'data-test-id': 'scroll-element',
+    } as ScrollableProps)?.domNode!;
+
+    // defineProperty needed to assign values to readonly node properties
+    Object.defineProperty(scrollNode, 'clientHeight', {get: () => 10});
+    Object.defineProperty(scrollNode, 'scrollHeight', {get: () => 10});
+    Object.defineProperty(scrollNode, 'scrollTop', {get: () => 10});
+
+    scrollArea.act(() => {
+      scrollNode.dispatchEvent(new Event('scroll'));
+    });
+
+    expect(onScrolledToBottom).not.toHaveBeenCalled();
+  });
 });

polaris-react/tests/setup/tests.ts

@@ -6,3 +6,8 @@ import './matchers';
 afterEach(() => {
   destroyAll();
 });
+
+globalThis.requestAnimationFrame = (cb) => {
+  cb(Date.now());
+  return Math.random();
+};