I am testing an image processing app and as such proper testing requires seletion of various images at runtime. Testing on a local device involves moving images on the local device and testing with an automated espresso UI test. How can I replicate this on the Firebase test lab devices? Is it possible?
Having a selection of files appear on the device prior to running tests is currently not possible with the tooling you're given, though I have recently discussed this with the team. I would encourage you to file a feature request describing your use case in order to add weight to the argument.
In the meantime, consider placing your images in the APK as some sort of resource, and write code to copy those into place during your test.