How to use files in instrumented unit tests

Question

I've got this project which processes images. The library I use to do most of the actual image processing requires me to run these tests on a Android device or emulator. I'd like to provide a few test images which it should process, the thing is that I don't know how to include these files in the androidTest APK. I could supply the images through the context/resources but I'd rather not pollute my projects resources. Any suggestions as to how to supply and use files in instrumented unit tests?

Answer 1

You can read asset files that are in your src/androidTest/assets directory with the following code:

Context testContext = InstrumentationRegistry.getInstrumentation().getContext();
InputStream testInput = testContext.getAssets().open("sometestfile.txt");

It is important to use the test's context as opposed to the instrumented application.

So to read an image file from the test asset directory you could do something like this:

public Bitmap getBitmapFromTestAssets(String fileName) {
   Context testContext = InstrumentationRegistry.getInstrumentation().getContext();
   AssetManager assetManager = testContext.getAssets();

   InputStream testInput = assetManager.open(fileName);
   Bitmap bitmap = BitmapFactory.decodeStream(testInput);

   return bitmap;
}