Support a FakeImageLoader for typical Preview use cases

[Yuri Schimke]

The https://coil-kt.github.io/coil/image_loaders/#testing docs suggest implementing a custom ImageLoader.

But there could be some useful defaults, like loading DrawableRes, or mapping a url to a test image.

https://github.com/google/horologist/blob/fdc4fa6b4bb4387c2ec7804a9c5eb9c67f909764/tiles/src/androidTest/java/com/google/android/horologist/tiles/FakeImageLoader.kt

It would be nice to have a Test or Fake ImageLoader that implemented sensible defaults for situations like Previews.

Would this be accepted as a PR?

[Colin White]

I agree, having a coil-fakeimageloader artifact (or similar) would be useful. I've been a bit cautious to add a 1st party artifact for it since it would require ongoing support vs. providing a recipe that can be copied + modified.

I'm going on holiday until the end of July so let's circle back on this then!

[Colin White]

@yschimke Took an initial stab at this here. It's not finished, but let me know if you have any feedback!

[Yuri Schimke]

I've ended up with this for testing smaller components that use Coil but won't explicitly see an Image Loader. Is this in scope?

    public inline fun ImageLoader.override(function: () -> Unit) {
        Coil.setImageLoader(this)
        try {
            function()
        } finally {
            Coil::class.java.getDeclaredField("imageLoader").apply {
                isAccessible = true
            }.set(null, null)
        }
    }

Or some other way to achieve this?