Scala

Scala testing with ScalaTest and Mockito

• Show me the code
  • Implementation
  • Test
• Run this project using 🐳 docker
• Run this project locally

Show me the code

Implementation

1. Create HelloMessage class in HelloMessage.scala:

class HelloMessage:
  def text: String = "Hello World!"

We can create it as a class as Mockito is able to mock final classes.

2. Same way create HelloConsole class in HelloConsole.scala:

class HelloConsole:
  def print(text: String): Unit =
    println(text)

3. Create HelloApp class in HelloApp.scala:

class HelloApp(message: HelloMessage, console: HelloConsole):
  def printHello(): Unit =
    console.print(message.text)

4. Create main class in Main.scala that wraps it all together:

@main def main(): Unit =
  val message = HelloMessage()
  val console = HelloConsole()
  val app = HelloApp(message, console)
  app.printHello()

Test

Following ScalaTest > Writing your first test and ScalaTest + Mockito guides ...

1. Test HelloMessage in HelloMessageSpec.scala:

class HelloMessageSpec extends AnyFlatSpec {

  "A HelloMessage" should "return hello world" in {
    val message = HelloMessage()
    assertResult(message.text) {
      "Hello World!"
    }
  }
}

2. Test HelloApp in HelloAppSpec.scala:

class HelloAppSpec extends AnyFlatSpec {

  "A HelloApp" should "print hello message" in {
    val messageText = "Hello Test!"

    // 2.1 Create a mock of HelloMessage
    val message = mock[HelloMessage]
    // 2.2 Return "Hello Test!" whenever text is called
    when(message.text).thenReturn(messageText)

    // 2.3 Create a mock of HelloConsole
    val console = mock[HelloConsole]

    // 2.4 Create a HelloApp, the one we want to test, passing the mocks
    val app = HelloApp(message, console)
    // 2.5 Execute the method we want to test
    app.printHello()

    // 2.6 Verify HelloConsole mock print() method
    // has been called once with "Hello Test!"
    verify(console).print(messageText)
  }
}

3. Test output should look like:

[info] HelloMessageSpec:
[info] A HelloMessage
[info] - should return hello world
[info] HelloAppSpec:
[info] A HelloApp
[info] - should print hello message
[info] Run completed in 515 milliseconds.
[info] Total number of tests run: 2
[info] Suites: completed 2, aborted 0
[info] Tests: succeeded 2, failed 0, canceled 0, ignored 0, pending 0
[info] All tests passed.
[success] Total time: 6 s

Run this project using 🐳 docker

• Execute ./docker-run.sh
• Once inside the container:
  • Test with sbt test
  • Run with sbt run

Run this project locally

Pre-requisites

• Install Java manually or ...
  • Install SdkMan and ...
    • List available versions executing sdk list java
• Install Scala
  • Install Coursier and execute cs install scala:3.3.1

Run locally

• Test with sbt test
• Run with sbt run

Create project from scratch

• Create project using sbt new scala/scala3.g8 (⚠️ maybe you get an error with Java 21 and you'll need Java 17 just for this step)
• Add ScalaTest and Mockito dependencies in build.sbt:

libraryDependencies += "org.scalatest" %% "scalatest" % "3.2.17" % Test,
libraryDependencies += "org.scalatestplus" %% "mockito-4-11" % "3.2.17.0" % Test

💡 Alternatively you can create a project using Gradle Scala Application Sample