Configuration

Kotest provides for the ability to specify some configuration options when running a property test. We do this by passing in an instance of PropTestConfig to the test methods.

For example:

class PropertyExample: StringSpec({
   "String size" {
      forAll<String, String>(PropTestConfig(options here...)) { a,b ->
         (a + b).length == a.length + b.length
      }
   }
})

Seed

A commonly used configuration option is specifying the seed used by the random source. This is used when you want to repeat the same values each time the test is run. You might want to do this if you find a test failure, and you want to ensure that that particular set of values continues to be executed in the future as a regression test.

For full details on how the seed is used click here.

Min Failure

By default, Kotest tolerates no failure. Perhaps you want to run some non-deterministic test a bunch of times, and you're happy to accept some small number of failures. You can specify that in config.

class PropertyExample: StringSpec({
   "some flakey test" {
      forAll<String, String>(PropTestConfig(maxFailure = 3)) { a,b ->
         // max of 3 inputs can fail
      }
   }
})

PropTestListener

Sometimes in property test it is required to perform some setup and tear down in each iteration of test. For this purpose you can register a PropTestListener with PropTestConfig.

class PropertyExample: StringSpec({
   "some property test which require setup and tear down in each iteration" {
      forAll<String, String>(PropTestConfig(listeners = listOf(MyPropTestListener))) { a,b ->
         // some assertion
      }
   }
})