I am attempting to fire a load event where the target property in the load event is customised.

test:

 const onLoad: ImageSrcSetProps['onLoad'] = (e, options) => void vi.fn(e, options);
 // pass the mock to the component to ensure it's called correctly when the image loads
 renderWithProviders(<ImageSrcSet {...getProps({ onLoad })} />);
 // crux of issue:
 const image = screen.getByRole('img'); 
 fireEvent.load(image, { target: { currentSrc: 'foo' } }); // you can't do this.

component

  const handleOnLoad = useCallback(
    (e: React.MouseEvent<HTMLImageElement>) => {
      console.log('currentSrc!!!--->', e.target.currentSrc, '<----');
    },
    [onLoad]
  );
  ...
 <img
   srcSet={getImageSrcSet}
   src={placeholderGif}
   role="img"
   onLoad={handleOnLoad}
 />

( The currentSrc is the image that the browser loaded – it varies based on screen size )

I have tried:

Object.defineProperty(global.Image.prototype, 'currentSrc', {
  writable: true,
});

But this will break vitest ( and probably jest too )

Error: Uncaught [Error: cannot spy on a non-function value] which is caused by mock `onLoad`

So yeah, catch-22 and stuck. Suggestions?