IssueTracker

Library used (Espresso, Runner, Rules etc.): espresso-core, espresso-idling-resource
Version used: 3.0.1

What steps will reproduce the problem?
1. register CountingIdlingResource in IdlingRegistry.getInstance().register()
2. launch Activity in test which performs some async operation (in worker thread which is monitored by CountingIdlingResource registered in previous step )
3. dont't use any of Espresso.onView, onData, registerIdlingResources
4. use Espresso.onIdle to check something not related with UI which should happen after async operation


How are you running your tests (via Android Studio, Gradle, adb, etc.)?
Android Studio


What is the expected output? What do you see instead?

Expected: test passed
Actual: test fail because onIdle does not wait for CountingIdlingResource

Reason:
Espresso registers IdlingResource's from IdlingRegistry to IdlingResourceRegistry by nvoking IdlingResourceRegistry.sync method. It does not invoke it in onIdle.
Everything works as expected if before onIdle there is Espresso.onView call.