Android Studio androidTest sourceSets gradle not recognized

Android Studio (app) build.gradle sourceSets androidTest java.srcDir property may not be recognized when using the array format of this source directory property setting.

BAD

sourceSets {
    androidTest {
        java.srcDirs = ['androidTest/java']
    }
}

GOOD

sourceSets {
    androidTest {
        java.srcDir file('androidTest/java')
    }
}

For setting up Robotium UI / Integration testing, it’s important that your androidTest source directory is recognized.