How to wait toast to showed up

I would like to create androidTest for my app. I've started with the login module witch contains multiple fragments and end with a new activity (in another module).

The last screen of login module start a CoroutineWorker to fetch data from our API. The user can see the progress of the worker through a notification. At the end of the worker (takes 30s to 5min), a toast appear with a message : "Success" or "fail"

So, when the test come to the new activity, I would like to wait this toast and check if the message is "Success"

I used this code to check the toast (using UiAutomator and Espresso)

private val uiDevice = UiDevice.getInstance(InstrumentationRegistry.getInstrumentation())

uiDevice.wait(Until.hasObject(By.text("Synchronization finished")), 20000)

For some reason, espresso end the test before the end of the worker, I'm guessing this is because the app is idling but I'm not sure.