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Effective Unit and Integration Testing in Scala

Checking Stateful Properties with ScalaCheck

Explore how to test mutable components using ScalaCheck by modeling commands and states to validate behavior over time. Understand how to define commands for state changes and verify system state, ensuring robust property-based testing of stateful Scala components.

We'll cover the following...

In this lesson, we’ll see how to test mutable or stateful components using ScalaCheck. Even if immutable components are often easier to use and understand, our applications sometimes need to use mutable components. Some components in Scala might look immutable to their users, but internally their implementation might make use of a mutable state.

With ScalaCheck we can test the behavior of a mutable component. In other words, we can see how the methods affect the state of the component over time. ScalaCheck defines a library to model commands that we can use to ensure the validity of our properties.

Modeling method invocation through commands

Modeling commands in ScalaCheck can be complex. In this lesson, we’ll test the following implementation of MutableEducative.

Scala
package mdipirro.educative.io.effectiveunitandintegrationtestinginscala.model.v2.mutable
import mdipirro.educative.io.effectiveunitandintegrationtestinginscala.model.v2.Course
class MutableEducative(var courses: Seq[Course]):
  def courseByName(courseTitle: String): Option[Course] = courses find (_.title == courseTitle)
  infix def `with`(newCourse: Course): Either[String, MutableEducative] =
    courses find (_.title.equalsIgnoreCase(newCourse.title)) match
      case Some(_) => Left(s"A course with title ${newCourse.title} already exists")
      case None =>
        courses = courses :+ newCourse
        Right(this)
  infix def without(courseTitle: String): MutableEducative =
    courses = courses filterNot (_.title.equalsIgnoreCase(courseTitle))
    this

We’ll test the interactions between the with and without methods. For clarity we’ll explain relevant snippets of code step by step. You’ll find the complete test suite at the end of the lesson.

Everything starts from the Commands ...