Android Studio - Unit Testing - Gradle Files

app.gradle

apply plugin: 'com.android.application'
 
android {
    // ...
}
 
dependencies {
    compile(project(':lib'))
}

lib.gradle

apply plugin: 'java'
 
dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    testCompile 'junit:junit:4.12'
    testCompile 'org.mockito:mockito-core:1.9.5'
}

project.gradle

buildscript {
    // ...
    
    dependencies {
        classpath 'com.android.tools.build:gradle:1.2.3'
    }
}
 
allprojects {
    // ...
}