ATDD, Generating random tests with ScalaCheck

Further, in our series on Acceptance Test Driven Development, we would look at generating random test values with the ScalaCheck framework. In our last post we looked at, how we make our test logic respect the DRY principle by defining the values in a table. However, in many situations, you would like to generate the values dynamically so that we do not have to fill a lot of values in the table. Let us see how this is done with the help of a library called ScalaCheck

We would change our test case a bit for dynamic value generation. Look at the code sample below

The important thing to note here is the trait called GeneratorDrivenPropertyChecks. This trait facilitates property checks against generated data using ScalaCheck.

In order to include ScalaCheck library in your project, we would need to include the following dependency

Let us look at the complete code sample

As you would notice, most of the things are quite the same as in our last example where we were using TableDrivenPropertyChecks. The difference being that now, instead of using Table driven values, we end up Generating values.

This code generates numbers between the given range. So it is -10 to 300 for validNumberOnes and between 10 to 15 for validNumberTwos.

Trait GeneratorDrivenPropertyChecks contains forAll method that provides various ways to check properties using generated data. Here, we are not only getting values of valiNumberOnes and validNumberTwos but also specifying the configuration parameters like minSuccessful, maxDiscarded and workers

Notice that the software under test in this case is the ActualBusinessImplementation class.

When we execute it, the system runs 500 successful tests with various value combinations and hence we know that the result is correct. The output of the evaluation would look something like this.

The ordering of the output looks a little weird because we are running the evaluation with four threads. As always the code is present on the Knoldus Github account.

Hence, as we saw it is easy to generate values with ScalaCheck and pass it to our test case. We can also specify the minimum number of generated value test which would need to be performed before we say that our code is good. In a follow up post to this ATDD series, we would look at another interesting candidate which would make life easy for stakeholders and developers. Till then.

Written by 

Vikas is the CEO and Co-Founder of Knoldus Inc. Knoldus does niche Reactive and Big Data product development on Scala, Spark, and Functional Java. Knoldus has a strong focus on software craftsmanship which ensures high-quality software development. It partners with the best in the industry like Lightbend (Scala Ecosystem), Databricks (Spark Ecosystem), Confluent (Kafka) and Datastax (Cassandra). Vikas has been working in the cutting edge tech industry for 20+ years. He was an ardent fan of Java with multiple high load enterprise systems to boast of till he met Scala. His current passions include utilizing the power of Scala, Akka and Play to make Reactive and Big Data systems for niche startups and enterprises who would like to change the way software is developed. To know more, send a mail to or visit

1 thought on “ATDD, Generating random tests with ScalaCheck

  1. “val validNumberOnes = for (n n)”. In this case you can simply write “val validNumberOnes = Gen.choose(-10, 300)”.

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