core build.gradle https://hackernoon.com/yet-another-mvp-article-part-1-lets-get-to-know-the-project-d3fd553b3e21

build.gradle

apply plugin: 'java'
/*...*/

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile rootProject.ext.libraries.rxjava

    testCompile rootProject.ext.testLibraries.junit
    testCompile rootProject.ext.testLibraries.mockito

    compile rootProject.ext.libraries.retrofit
    
    /*...*/
}