Why is IdlingResource null in Espresso tests?

I am setting up espresso tests for my Android with an IdlingResource identical to the example here.
My Test setup:

@Rule
public ActivityTestRule<MainActivity> mMainActivity =
        new ActivityTestRule(MainActivity.class);

private IdlingResource mIdlingResource;

@Before
public void registerIdlingResource() {
    mIdlingResource = mMainActivity.getActivity().getIdlingResource();
    IdlingRegistry.getInstance().register(mIdlingResource);
}

In my Activity each time I change the Idle state I call:

if (mIdlingResource != null) {
    mIdlingResource.setIdleState(false);
} else {
    Log.d("error ", "idle resource is null");
}

My issue comes when trying to change the idle state in my activity -- there seems to be a lag between when the activity is created and the IdlingResource is available.
In the first test of the sequence, the IdlingResource is never available -- as such I cannot set the initialValue of the IdlingResource to false and then later switch back to true. That seems to be caused by the annotation lifecycle as described in this article:

From what I can tell the Activity is created by the @Rule and then the IdlingResource is instantiated in the @Before. Since the Activity is already running the idle resource is null at each of the points where I attempt to change the state.
In subsequent tests only the first instance of setIdleState (which occurs in the onCreate) is skipped -- perhaps something to do with the Activity lifecycle with the @Rule? -- but the others operate as expected.
Is there a best practice to getting the @Rule and @Before to work in order before the first test?


from Why is IdlingResource null in Espresso tests?