JUnit4 is the old JUnit system that was last updated way back in 2014. JUnit5 brings many new improvements, but at the moment it is tough to use it on Android.

There is 3rd party gradle plugin that supports JUnit5: https://github.com/mannodermaus/android-junit5 and while it works fine, it especially lacks in UI rules like in ActivityRule or ServiceRule (All official rules are for JUnit4, so they have to be rewritten if one wants to use JUnit5 for instrumentation tests).

(Copied from https://issuetracker.google.com/issues/127100532)