Add dependency to build.gradle in your app module

    testImplementation 'org.robolectric:robolectric:4.2'
    testImplementation 'androidx.test:core:1.0.0'

• Robolectric - official website
• Set up project for AndroidX Test
• ShadowTelephonyManagerTest.java
• Shadows
• [Android] Unit Testing Framework - Robolectric
• Robolectric Unit Test Sample Code for Android
• http://robolectric.org/blog/2019/06/04/paused-looper/Improving Robolectric's Looper simulation