scalacheck

Reproducing a ScalaCheck test run

This was asked as a "bonus question" in https://stackoverflow.com/questions/12639454/make-scalacheck-tests-deterministic, but not answered:

Is there a way to print out the random seed used by ScalaCheck, so that you can reproduce a specific test run?

There is a hacky way: wrap a random generator to print its seed on initialization and pass it to Test.Parameters. Is there a better option?

Solution

  • As of today, this is possible (see scalacheck#263). There are some nice examples here: Simple example of using seeds with ScalaCheck for deterministic property-based testing.

    In short, you can do:

    propertyWithSeed("your property", Some("seed")) =
  forAll { ??? }

    and the seed will be printed when this property fails.