Skip to main content
Version: 5.8

Extension Examples

System Out Listener​

A real example of an extension, is the NoSystemOutListener which comes with Kotest. This extension throws an error if any output is written to standard out.

class MyTestSpec : DescribeSpec({

listener(NoSystemOutListener)

describe("All these tests should not write to standard out") {
it("silence in the court") {
println("boom") // failure
}
}
})

Timer Listener​

Another example would be if we wanted to log the time taken for each test case. We can do this by using the beforeTest and afterTest functions as follows:

object TimerListener : BeforeTestListener, AfterTestListener {

var started = 0L

override fun beforeTest(testCase: TestCase): Unit {
started = System.currentTimeMillis()
}

override fun afterTest(testCase: TestCase, result: TestResult): Unit {
println("Duration of ${testCase.descriptor} = " + (System.currentTimeMillis() - started))
}
}

Then we can register like so:

class MyTestClass : FunSpec({
extensions(TimerListener)
// tests here
})

Or we could register it project wide:

object MyConfig : AbstractProjectConfig() {
override fun extensions(): List<Extension> = listOf(TimerListener)
}