Coil: Idling resource for espresso

[AchrafAmil]

Is your feature request related to a problem? Please describe.
Espresso UI tests that do depend on images loading, for instance before taking screenshot or asserting some bitmap computation.

Describe the solution you'd like
In order to signal ongoing image loading to Espresso, Coil can expose an IdlingResource.

Additional context
Glide and Picasso doesn't provide an out-of-the-box solution but workarounds exist:
https://lcdsmao.dev/synchronize-glide-loading-in-test-with-idlingresource/
https://gist.github.com/sebaslogen/0b2fdea3f322c730e04b0af7285fcd28

[R4md4c]

Wouldn't that be solved by wrapping your CoroutineDispatcher around an IdlingThreadPoolExecutor?

Something like:

private val idlingThreadPool = IdlingThreadPoolExecutor(
        "coroutinesDispatchersThreadPool",
        Runtime.getRuntime().availableProcessors(),
        Runtime.getRuntime().availableProcessors(),
        0L,
        TimeUnit.MILLISECONDS,
        LinkedBlockingQueue(),
        Executors.defaultThreadFactory()
    )

And when you build your ImageLoader instance

override fun newImageLoader(): ImageLoader =
        ImageLoader.Builder(context)
            .dispatcher(idlingThreadPool.asCoroutineDispatcher()) 
           .build()

[AchrafAmil]

Indeed, will try that. Didn't know about IdlingThreadPoolExecutor, it seems to solve the problem in an even better way.

Thanks, issue to be closed.