Today I learned... Data-driven unit testing in Scala

I've done data-driven unit tests in C# before, but recently I learned how to do them in Scala, and it's very easy and clean.

An example unit test, using WordSpec, which follows a BDD-style syntax, is below:

"Multiplying two integers" when {
  "one is negative" should {
    "have a negative result" in {
      val positive = scala.util.Random.nextInt(10000)
      val negative = -1 * scala.util.Random.nextInt(10000)
      val result = positive * negative
      assert(result < 0, s"positive * negative should be negative, but is ${result}!")
    }
  }
}

Unit test methods can be created on-the-fly at runtime, and therefore you can take any data source and turn it into a set of unit tests. Here is an example using WordSpec, which is one of the several flavors of writing unit tests in Scala.

(1 to 100).foreach(testCaseNumber => {
  s"Test scenario $testCaseNumber" when {
    "doing something" should {
      "return success" in {
        doSomethingWithData(getDataForTest(testCaseNumber))
      }
    }
  }
}

When you run all unit tests in your class, ScalaTest will show each of these 100 data as a separate test case with separate pass/fails.

It's really slick, and if you have some common test that you want to run over and over with some slight modification that can be controlled based on some parameter, I recommend you give it a try!