Update unit tests

- to work around new non-jest/jsdom-friendly behavior

src/components/selectable/selectable_list/selectable_list.test.tsx

@@ -362,6 +362,13 @@ describe('EuiSelectableListItem', () => {
   });
 
   describe('truncation performance optimization', () => {
+    // Mock requestAnimationFrame
+    beforeEach(() => {
+      jest
+        .spyOn(window, 'requestAnimationFrame')
+        .mockImplementation((cb: Function) => cb());
+    });
+
     it('does not render EuiTextTruncate if not virtualized and text is wrapping', () => {
       const { container } = render(
         <EuiSelectableList
@@ -395,6 +402,12 @@ describe('EuiSelectableListItem', () => {
     });
 
     it('attempts to use a default optimized option width calculated from the wrapping EuiAutoSizer', () => {
+      // jsdom doesn't return valid element offsetWidths, so we have to mock it here
+      Object.defineProperty(HTMLElement.prototype, 'offsetWidth', {
+        configurable: true,
+        value: 600,
+      });
+
       const { container } = render(
         <EuiSelectableList
           options={options}