build.gradle

buildscript {
    repositories {
        maven { url "https://plugins.gradle.org/m2/" }
    }
    dependencies {
        classpath 'org.jetbrains.kotlin:kotlin-gradle-plugin:1.2.20'
        classpath 'com.moowork.gradle:gradle-node-plugin:1.2.0'
    }
}

apply plugin: 'kotlin2js'
apply plugin: 'com.moowork.node'

repositories {
    jcenter()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-js"
    testCompile "org.jetbrains.kotlin:kotlin-test-js"
}

[compileKotlin2Js, compileTestKotlin2Js]*.configure {
    kotlinOptions.moduleKind = "commonjs"
}

task populateNodeModules(type: Copy, dependsOn: compileKotlin2Js) {
   from compileKotlin2Js.destinationDir

   configurations.testCompile.each {
       from zipTree(it.absolutePath).matching { include '*.js' }
   }

   into "${buildDir}/node_modules"
}

node { 
  download = true
}

task installMocha(type: NpmTask) {
    args = ['install', 'mocha']
}

task runMocha(type: NodeTask, dependsOn: [compileTestKotlin2Js, populateNodeModules, installMocha]) {
    script = file('./node_modules/mocha/bin/mocha')
    args = [compileTestKotlin2Js.outputFile]
}

test.dependsOn runMocha