Using UiAutomator to test if map has loaded or not

I am new to testing in android. I have a map activity, which is called after some events in the MainActivity and a map appears in the screen. I am not able to figure out how to test whether the map appears or not. I understand its not possible with espresso, but have read somewhere that its possible with UiAutomator. How to use UiAutomator for the same..?