For an instrumentation test on Bitrise Virtual Device Testing, you'll need two APKs, as it seems to be a Firebase TestLab constraint:
But if you are developing only a library and not a whole app, you won't have both, only the test one. Trying to use the test APKs in both inputs (APK Path and Test APK Path) is futile as it'll return the following error message:
To be able to test your library, you'll need to use the regular test APK which includes the library, and as a workaround, generate a dummy APK and set that as the app APK. Basically, any APK will do, but if you need one, check out our sample apps on GitHub. 🙂
Learn how to test an Android library on Bitrise's Virtual Device Testing.