testing-scala-in-intellij-with-scalatest.md

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There are multiple libraries and testing methodologies for Scala, but in this tutorial, we'll demonstrate one popular option from the ScalaTest framework called FunSuite.

This assumes you know how to build a project in IntelliJ.

Setup

1. Create an sbt project in IntelliJ.
2. Add the ScalaTest dependency:
   1. Add the ScalaTest dependency to your build.sbt file:

      libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.8" % Test
      

   2. If you get a notification "build.sbt was changed", select auto-import.
   3. These two actions will cause sbt to download the ScalaTest library.
   4. Wait for the sbt sync to finish; otherwise, FunSuite and test() will be unrecognized.
3. On the project pane on the left, expand src => main.
4. Right-click on scala and select New => Scala class.
5. Call it CubeCalculator, change the Kind to object, and click OK.
6. Replace the code with the following:

   object CubeCalculator extends App {
     def cube(x: Int) = {
       x * x * x
     }
   }
   

Creating a test

1. On the project pane on the left, expand src => test.
2. Right-click on scala and select New => Scala class.
3. Name the class CubeCalculatorTest and click OK.
4. Replace the code with the following:

   import org.scalatest.FunSuite
   
   class CubeCalculatorTest extends FunSuite {
     test("CubeCalculator.cube") {
       assert(CubeCalculator.cube(3) === 27)
     }
   }
   

5. In the source code, right-click CubeCalculatorTest and select Run 'CubeCalculatorTest'.

Understanding the code

Let's go over this line by line:

• class CubeCalculatorTest means we are testing the object CubeCalculator
• extends FunSuite lets us use functionality of ScalaTest's FunSuite class such as the test function
• test is function that comes from the FunSuite library that collects results from assertions within the function body.
• "CubeCalculator.cube" is a name for the test. You can call it anything but one convention is "ClassName.methodName".
• assert takes a boolean condition and determines whether the test passes or fails.
• CubeCalculator.cube(3) === 27 checks whether the output of the cube function is indeed 27. The === is part of ScalaTest and provides clean error messages.

Adding another test case

1. Add another assert statement after the first one that checks for the cube of 0.
2. Re-run the test again by right-clicking CubeCalculatorTest and selecting 'Run CubeCalculatorTest'.

Conclusion

You've seen one way to test your Scala code. You can learn more about ScalaTest's FunSuite on the official website.