To test device scale, run chrome with --force-device-scale-factor=2 (or run chrome on a device with > 1 device scale, such as a macbook running in high dpi mode)

Select some text and start dragging. If the text in the drag image is rendered at the same size as the text on the page and is not blurry (due to scaling), 1st part of this test passes.

For 2nd part, try dragging "Drag me" below. Again, if the text in the drag image is rendered at the same size as the text on the page is not blurry, the test passes.

Drag me

Lastly, for testing dragging of images, drag the image below. If drag image is exactly the same size as the image on the page, the test passes.