Testing Scala with sbt and ScalaTest on the Command Line

There are multiple libraries and testing methodologies for Scala, but in this tutorial, we’ll demonstrate one popular option from the ScalaTest framework called AnyFunSuite. We assume you know how to create a Scala project with sbt.

Setup

1. On the command line, create a new directory somewhere.
2. cd into the directory and run sbt new scala/scalatest-example.g8
3. Name the project ScalaTestTutorial.
4. The project comes with ScalaTest as a dependency in the build.sbt file.
5. cd into the directory and run sbt test. This will run the test suite CubeCalculatorTest with a single test called CubeCalculator.cube.

sbt test
[info] Loading global plugins from /Users/username/.sbt/0.13/plugins
[info] Loading project definition from /Users/username/workspace/sandbox/my-something-project/project
[info] Set current project to scalatest-example (in build file:/Users/username/workspace/sandbox/my-something-project/)
[info] CubeCalculatorTest:
[info] - CubeCalculator.cube
[info] Run completed in 267 milliseconds.
[info] Total number of tests run: 1
[info] Suites: completed 1, aborted 0
[info] Tests: succeeded 1, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[success] Total time: 1 s, completed Feb 2, 2017 7:37:31 PM

Understanding tests

1. Open up two files in a text editor:
   • src/main/scala/CubeCalculator.scala
   • src/test/scala/CubeCalculatorTest.scala
2. In the file CubeCalculator.scala, you’ll see how we define the function cube.
3. In the file CubeCalculatorTest.scala, you’ll see that we have a class named after the object we’re testing.

  import org.scalatest.funsuite.AnyFunSuite

  class CubeCalculatorTest extends AnyFunSuite {
      test("CubeCalculator.cube") {
          assert(CubeCalculator.cube(3) === 27)
      }
  }

Let’s go over this line by line.

• class CubeCalculatorTest means we are testing the object CubeCalculator
• extends AnyFunSuite lets us use functionality of ScalaTest’s AnyFunSuite class such as the test function
• test is function that comes from AnyFunSuite 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 test block with its own assert statement that checks for the cube of 0.

      import org.scalatest.funsuite.AnyFunSuite
       
      class CubeCalculatorTest extends AnyFunSuite {
          test("CubeCalculator.cube 3 should be 27") {
              assert(CubeCalculator.cube(3) === 27)
          }
   
          test("CubeCalculator.cube 0 should be 0") {
              assert(CubeCalculator.cube(0) === 0)
          }
      }
   

2. Execute sbt test again to see the results.

    sbt test
    [info] Loading project definition from C:\projects\scalaPlayground\scalatestpractice\project
    [info] Loading settings for project root from build.sbt ...
    [info] Set current project to scalatest-example (in build file:/C:/projects/scalaPlayground/scalatestpractice/)
    [info] Compiling 1 Scala source to C:\projects\scalaPlayground\scalatestpractice\target\scala-2.13\test-classes ...
    [info] CubeCalculatorTest:
    [info] - CubeCalculator.cube 3 should be 27
    [info] - CubeCalculator.cube 0 should be 0
    [info] Run completed in 257 milliseconds.
    [info] Total number of tests run: 2
    [info] Suites: completed 1, aborted 0
    [info] Tests: succeeded 2, failed 0, canceled 0, ignored 0, pending 0
    [info] All tests passed.
    [success] Total time: 3 s, completed Dec 4, 2019 10:34:04 PM
   

Conclusion

You’ve seen one way to test your Scala code. You can learn more about ScalaTest’s FunSuite on the official website. You can also check out other testing frameworks such as ScalaCheck and Specs2.