append a base element to force the baseURI of the FakeWindow (#40218)

extensions/amp-skimlinks/0.1/test/test-affiliate-link-resolver.js

@@ -396,8 +396,7 @@ describes.fakeWin(
           expect(resolver.getAnchorDomain_(anchor)).to.equal('test.com');
         });
 
-        // TODO(#40214): fix flaky test.
-        it.skip('removes // protocol', () => {
+        it('removes // protocol', () => {
           const anchor = helpers.createAnchor('//test.com/');
           expect(resolver.getAnchorDomain_(anchor)).to.equal('test.com');
         });

extensions/amp-story-player/0.1/test/test-e2e/test-amp-story-player.js

@@ -22,8 +22,7 @@ describes.endtoend(
       await expect(player);
     });
 
-    // TODO(#40214): fix flaky test.
-    it.skip('loads and displays first story on page load when player is visible in viewport', async () => {
+    it('loads and displays first story on page load when player is visible in viewport', async () => {
       const shadowHost = await controller.findElement(
         'div.i-amphtml-story-player-shadow-root-intermediary'
       );

extensions/amp-video/0.1/test/test-flexible-bitrate.js

@@ -47,8 +47,7 @@ describes.fakeWin('amp-video flexible-bitrate', {}, (env) => {
       expect(currentBitrates(v0)[0]).to.equal(1000);
     });
 
-    // TODO(#40214): fix flaky test.
-    it.skip('should observe lower bandwidth on next sort', () => {
+    it('should observe lower bandwidth on next sort', () => {
       const m = getManager('4g');
       const v0 = getVideo([4000, 1000, 3000, 2000]);
       v0.id = 'v0';

testing/fake-dom.js

@@ -71,6 +71,14 @@ export class FakeWindow {
     // Document.
     /** @const {!HTMLDocument} */
     this.document = self.document.implementation.createHTMLDocument('');
+    // NOTE: There was a change between chrome 119 and 120 where the above
+    // self.document.implementation.createHTMLDocument no longer inherits
+    // the baseURI of self.document. We explicitly set and force it thru
+    // a `<base>` element.
+    const base = this.document.createElement('base');
+    base.href = self.document.baseURI;
+    this.document.head.appendChild(base);
+
     Object.defineProperty(this.document, 'defaultView', {
       get: () => this,
     });