App.kt

/*                                                                                   
* This Kotlin source file was generated by the Gradle 'init' task.
*/
package KatakanaRomajiConvert

import com.ibm.icu.text.Transliterator

class KatakanaRomajiConvert(val word: String = "") {
  val katakanaToRomaji: String
  get(): String {
    val transliterator = Transliterator.getInstance("Katakana-Latin")
    return transliterator.transliterate(word)
  }
}

fun main(args: Array<String>) {
  if (args.size != 0) {
    val t = KatakanaRomajiConvert(args[0])
    println(t.katakanaToRomaji)
  } else {
    println("")
  }
}

AppTest.kt

/*
* This Kotlin source file was generated by the Gradle 'init' task.
*/
package KatakanaRomajiConvert

import kotlin.test.Test
import kotlin.test.assertEquals

class AppTest {
  @Test fun testAppHasAKatakanaArg() {
    val t = KatakanaRomajiConvert("トウキョウ")
    assertEquals("toukyou", t.katakanaToRomaji)
  }
  @Test fun testAppHasNoArg() {
    val t = KatakanaRomajiConvert()
    assertEquals("", t.katakanaToRomaji)
  }
  @Test fun testAppHasEmptyArg() {
    val t = KatakanaRomajiConvert("")
    assertEquals("", t.katakanaToRomaji)
  }
  @Test fun testAppHasMixCharStrArg() {
    val t = KatakanaRomajiConvert("あいうアイウabcＡＢＣ")
    assertEquals("あいうaiuabcＡＢＣ", t.katakanaToRomaji)
  }
  @Test fun testAppHasMixCharAndSpcStrArg() {
    val t = KatakanaRomajiConvert("あいう アイウ abc ＡＢＣ")
    assertEquals("あいう aiu abc ＡＢＣ", t.katakanaToRomaji)
  }
}

build.gradle.kts

/*
 * This file was generated by the Gradle 'init' task.
 *
 * This generated file contains a sample Kotlin application project to get you started.
 */
import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar

plugins {
    // Apply the Kotlin JVM plugin to add support for Kotlin on the JVM
    kotlin("jvm") version "1.3.10"

    // Apply the application to add support for building a CLI application
    id("application")
    id("com.github.johnrengelman.shadow") version "5.0.0"
}

repositories {
    // Use jcenter for resolving your dependencies.
    // You can declare any Maven/Ivy/file repository here.
    jcenter()
}

dependencies {
    // Use the Kotlin JDK 8 standard library
    implementation("org.jetbrains.kotlin:kotlin-stdlib-jdk8")

    // Use the Kotlin icu4j library
    implementation("com.ibm.icu:icu4j:63.1")

    // Use the Kotlin test library
    testImplementation("org.jetbrains.kotlin:kotlin-test")

    // Use the Kotlin JUnit integration
    testImplementation("org.jetbrains.kotlin:kotlin-test-junit")
}

application {
    // Define the main class for the application
    mainClassName = "KatakanaRomajiConvert.AppKt"
}

tasks.withType<Jar> {
    manifest {
        attributes(mapOf(
                "Main-Class" to "KatakanaRomajiConvert.AppKt"
        ))
    }
}

tasks.withType<ShadowJar> {
    baseName = "kana2romaji"
    classifier = ""
    version = ""
}

gradle.properties

org.gradle.jvmargs='-Dfile.encoding=UTF-8'
org.gradle.daemon=true
// org.gradle.java.home=C:\\JDKPortable
// systemProp.http.proxyHost=
// systemProp.http.proxyPort=
// systemProp.https.proxyHost=
// systemProp.https.proxyPort=