Using Scala to Test Your Java Projects

In this technical blog coder-in-residence Viktor Nordling describes a sample project he has developed to showcase the ScalaTest test framework.

The Mission

I’ve been planning on starting to learn Scala by developing tests for my existing Java projects using the Scala language (following the advice of Java Posse’s Dick Wall). I originally found this article on StackOverflow but it didn’t really answer my questions. I then read an excellent blog article from ex-colleague Frederik Tyboni that descibed exactly what I wanted to do. Unfortunately for alot of readers his article is in Swedish. So here follows a rough translation of what he wrote — along with an example project that I have developed and posted on GitHub. My goal is to get you started with ScalaTest in minutes!

For the impatient, the example project is here

Integrating ScalaTest into Your Existing Maven Build

Assuming you are using Maven, all you need to do is first add the dependencies for Scala, JUnit and ScalaTest, like so:

    org.scala-lang
    scala-library
    2.9.1
    test


    junit
    junit
    4.8.1
    test


    org.scalatest
    scalatest_2.9.1
    1.6.1
    test

Secondly, we add the maven-scala-plugin so that we can compile Scala code:

    org.scala-tools
    maven-scala-plugin
    2.15.0
    
        
            
                testCompile
            
            
                
                    -make:transitivenocp
                    -dependencyfile
                    ${project.build.directory}/.scala_dependencies
                
            
        
    

Now we tell the surefire-test-plugin to include **Spec files when executing tests:

    org.apache.maven.plugins
    maven-surefire-plugin
    2.6
    
        false
        true
        
            **/*Spec.*
            **/*Test.*
        
     

Finally, use the build-helper-plugin to tell Maven to include source files under src/test/scala when compiling the tests.

    org.codehaus.mojo
    build-helper-maven-plugin
    
        
            generate-test-sources
            generate-test-sources
            
                add-test-source

            
            
                
                    src/test/scala
                
            
        
    

All we have to do now is to add a test. If you want to, you can use JUnit. In this way, you can use the more expressive syntax of Scala to write your tests, while still being in the familiar land of JUnit.

Or, you can take one step further and try a Scala testing framework. Here’s an example using ScalaTest, which is a test framework that integrates with JUnit and TestNG. It supports BDD if you’re into that and will make your tests more expressive than standard JUnit tests.

package com.cubeia

import org.junit.runner.RunWith
import org.scalatest.matchers.MustMatchers
import org.scalatest.FlatSpec
import org.scalatest.junit.JUnitRunner

@RunWith(classOf[JUnitRunner])
class CalculatorSpec extends FlatSpec with MustMatchers {

  "Calculator" must "multiply two values" in {
    val calculator = new Calculator;
    calculator.multiply(3, 5) must equal (15)
  }
}

The Calculator class is written in Java, but tested from Scala. Again, you can get the source files for this if you clone my example project on GitHub.

That’s all! Happy Scala hacking!

—
Viktor is a freelance software engineer who occasionally finds coding serenity at the Agile Digital office.