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/preload-image-srcset-reverse-order.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/image1.png'); is false PASS internals.isPreloaded('resources/base-image1.png'); is true PASS internals.isPreloaded('resources/image2.png'); is true PASS successfullyParsed is true TEST COMPLETE This test passes if the fallback image (defined in the src attribute) is not preloaded, but the 1x version (defined in srcset) is, even when srcset is defined first. The second image is here to make sure isPreloaded is working properly