main frame - didStartProvisionalLoadForFrame main frame - didCommitLoadForFrame main frame - didFinishDocumentLoadForFrame main frame - didHandleOnloadEventsForFrame main frame - didFinishLoadForFrame main frame - didStartProvisionalLoadForFrame 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 src attribute) is not preloaded, but the 1x version (defined in srcset) is. The second image is here to make sure isPreloaded is working properly