tek / kallikrein

scala testing framework



kallikrein is a Scala testing framework for sbt focused on running cats-effect based programs.

If you're into matcher DSLs, check out xpct, which is a framework-agnostic typed matcher lib with support for kallikrein.

module ids

"io.tryp" %% "kallikrein-sbt" % "0.5.2"
"io.tryp" %% "kallikrein-http4s-sbt" % "0.5.2"


To use the framework in a project, specify the setting:

testFrameworks += new TestFramework("klk.KlkFramework")


Imperative DSL

class SomeTest
extends klk.IOTest
  test("description")(IO.pure(1 == 1))

Tests are added by calling the test function in a class inheriting klk.SimpleTest[F], where F[_] is an effect that implements cats.effect.Sync. klk.IOTest is a convenience trait using cats.effect.IO.

Assertions are returned from the test thunk and can be anything, as long as there is an instance for klk.TestResult. The internal type representing the result is KlkResult.

Composable Tests

The above mentioned test builder can also be used in a pure context and has a nice arsenal of typeclass instances for composition.

When tests are sequenced in a for comprehension, the semantic effect is that of conditional execution: If one test fails, all following tests are skipped.

There is an instance of SemigroupK available, allowing you to use the <+> operator, resulting in the alternative, or unless, semantics – i.e. if and only if the first test fails, execute the second one and use its result.

For independent tests, there are two combinators: sequential and parallel. They do what you would expect, similar to the imperative test building syntax. The parallel variant requires an instances of cats.Parallel and will execute the tests with a parTraverse.

The following example will result in a successful end result:

class DepTest
extends ComposeTest[IO, SbtResources]
  def testSuccess: IO[Boolean] =

  def testFail: IO[Boolean] =
    IO.raiseError(new Exception("boom"))

  implicit def cs: ContextShift[IO] =

  def tests: Suite[IO, Unit, Unit] =
    for {
      _ <- sharedResource(Resource.pure(5))(
        builder =>
          builder.test("five is 4")(five => IO.pure(five == 4)) <+>
          builder.test("five is 5")(five => IO.pure(five == 5))
      _ <- test("test 1")(testSuccess)
      _ <- test("test 2")(testFail) <+> test("test 3")(testSuccess)
      _ <- Suite.parallel(test("test 4a")(testSuccess), test("test 4b")(testSuccess)) <+> test("test 5")(testFail)
      _ <- test("test 7")(testSuccess)
    } yield ()

Results and Effects

The effect type of an individual test can be different from the main effect if there is an instance of klk.Compile[F, G]. For example, EitherT is supported out of the box:

test("EitherT")(EitherT.right[Unit](IO.pure(1 == 1)))

A Left value will be converted into a failure by the typeclass TestResult[A], meaning that this works just as well with IO[Either[A, B]].


A Stream[F, A] will automatically be compiled to F, with the inner value being handled by a dependent typeclass instance.


The kallikrein-http4s-sbt module provides a shared resource that runs an http4s server on a random port and supplies tests with a client and the Uri of the server wrapped in a test client interface:

class SomeTest
extends klk.Http4sTest[IO]
  def tests: Suite[IO, Unit, Unit] =
      .test { builder =>
      builder.test("http4s") { client =>
        client.fetch(Request[IO]())(_ => IO.pure(true))

The TestClient class provides a fetch method that injects the uri into the request with its withUri(request: Request[F]) method, as well as a success method, which produces a failed KlkResult if the response status is other than 2xx.


Tests can depend on shared and individual resources that will be supplied by the framework when running:

class SomeTest
extends klk.IOTest
  val res1: Resource[IO, Int] = Resource.pure(1)

  val res2: Resource[IO, Int] = Resource.pure(1)

  test("resource").resource(res1).resource(res2)((i: Int) => (j: Int) => IO.pure(i == j))

  def eightySix: SharedResource[IO, Int] =

  eightySix.test("shared resource 1")(i => IO.pure(i == 86))

  eightySix.test("shared resource 2")(i => IO.pure(i == 68))

The shared resource will be acquired only once and supplied to all tests that use it.

Property Testing

Scalacheck can be used in a test by calling the forall method on a test builder:

class SomeTest
extends klk.IOTest
  test("are all lists of integers shorter than 5 elements?").forall((l1: List[Int]) => IO(l1.size < 5))

This features a custom runner for the properties built on fs2.

A second variant forallNoShrink does what it advertises.

Law Checking

cats-discipline laws can be checked like this:

class SomeTest
extends klk.IOTest
  test("laws").laws(IO.pure(FunctorTests[List].functor[Int, Int, Int]))