Kotlin build.gradle (Android Module)

android.library.build.gradle

apply plugin: 'com.android.library'
apply plugin: 'kotlin-android'
apply plugin: 'kotlin-android-extensions'
apply plugin: 'kotlin-kapt'

android {
    compileSdkVersion 27
    defaultConfig {
        minSdkVersion 19
        targetSdkVersion 27
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }

    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
        }
    }

}

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'com.android.support:appcompat-v7:27.1.0'

    testImplementation 'junit:junit:4.12'
    testImplementation 'org.jetbrains.kotlin:kotlin-test-junit:1.2.30'
    testImplementation 'org.mockito:mockito-core:2.16.0'
    androidTestImplementation 'com.android.support.test:runner:1.0.1'
    androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.1'
}

kotlin.build.gradle

apply plugin: 'java'
apply plugin: 'kotlin'

dependencies {
    implementation fileTree(dir: 'libs', include: ['*.jar'])
    implementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.2.30'

    testImplementation 'junit:junit:4.12'
    testImplementation 'org.jetbrains.kotlin:kotlin-test-junit:1.2.30'
    testImplementation 'org.mockito:mockito-core:2.16.0'
}

repositories {
    mavenCentral()
}

compileKotlin {
    kotlinOptions {
        jvmTarget = "1.8"
    }
}
compileTestKotlin {
    kotlinOptions {
        jvmTarget = "1.8"
    }
}