main frame - DidStartNavigation main frame - ReadyToCommitNavigation main frame - didCommitLoadForFrame main frame - didFinishDocumentLoadForFrame main frame - didHandleOnloadEventsForFrame main frame - didFinishLoadForFrame main frame - BeginNavigation request to 'http://127.0.0.1:8000/loading/link-preload-image-srcset.html', http method GET main frame - DidStartNavigation main frame - ReadyToCommitNavigation main frame - didCommitLoadForFrame main frame - didFinishDocumentLoadForFrame main frame - didHandleOnloadEventsForFrame main frame - didFinishLoadForFrame PASS internals.isPreloaded('resources/preload-test.jpg'); is false PASS internals.isPreloaded('resources/base-image1.png'); is true PASS internals.isPreloaded('resources/base-image2.png'); is false PASS internals.isPreloaded('resources/base-image3.png'); is false PASS internals.isPreloaded('resources/image2.png'); is true PASS successfullyParsed is true TEST COMPLETE This test passes if the fallback image (defined in the href attribute) is not preloaded, but the 1x version (defined in imagesrcset) is. The second link rel=preload is here to make sure isPreloaded is working properly