getExternalFilesDir(null) returns null in Espresso tests

Issue

I'm trying to access getExternalFilesDir(null) from an Espresso test during the execution of a @BeforeClass method to set up some app files before starting tests.

I'm trying to access it like this: InstrumentationRegistry.getInstrumentation().context.getExternalFilesDir(null)

Environment.getExternalStorageState() returns "mounted", yet getExternalFilesDir(null) returns null in the above call, contrary to the documentation which states it would only return null if storage wasn't mounted.

Interestingly enough, InstrumentationRegistry.getInstrumentation().context.filesDir does return a value, but it returns a non-existent folder which is under a test package instead of the app's actual package.

How can I access and write to app's scoped storage when setting up an Espresso test?

Solution

InstrumentationRegistry.getInstrumentation().context gives you the context for the test APK. InstrumentationRegistry.getInstrumentation().targetContext gives you the context for the APK under test.

If the directory has not yet been created, getExternalFilesDir might return null the first time, so you may have to call it twice.

With targetSdk=30 on an API 30 emulator, this:

    companion object {
        @BeforeClass @JvmStatic
        fun beforeClass() {
            val targetContext = InstrumentationRegistry.getInstrumentation().targetContext
            Log.d("storage", targetContext.getExternalFilesDir(null).toString())
            Log.d("storage", targetContext.getExternalFilesDir(null).toString())
        }
    }

Will print this on first install/run:

D/storage: null
D/storage: /storage/emulated/0/Android/data/com.example.test/files

and this on the second run:

D/storage: /storage/emulated/0/Android/data/com.example.test/files
D/storage: /storage/emulated/0/Android/data/com.example.test/files

More on behavior with targetSdk=30:
https://developer.android.com/training/data-storage/use-cases#migrate-legacy-storage

Answered By - yogurtearl