cuzfrog / scala-jest   0.2.1

Apache License 2.0 GitHub

A lightweight scala.js test framework that brings back the power to test against jsdom within sbt console

Scala versions: 2.12
Scala.js versions: 0.6


Scala.js Build Status Maven Central

Write jest tests as scala classes and run them within sbt without any hassle.

Build against scala-2.12 and scalajs-0.6.22. (scalajs-0.6.22 speeds up test startup)


  • To workaround scala.js issue #2635.
  • To provide a better test ability against nodejs + jsdom + CommonJS on scala.js.
  • That is: test your scala.js-react project just by sbt test




  • nodejs (probably higher than v8.7.0)
  • package.json, or npm init to make one
  • npm install --save-dev jest-cli

See scala.js doc for file path conventions.


libraryDependencies += "com.github.cuzfrog" %%% "sjest" % "0.2.0" % Test

Provide test Framework(to specify client build info):

val myTestFramework: TestFramework = new TestFramework("sjest.JestFramework")
testFrameworks += myTestFramework
testOptions += Tests.Argument(myTestFramework,
  s"-opt.js.path:${(artifactPath in Test in fastOptJS).value}")

Scala-jest has to know where the *.opt.js file is. This can also be set through overriding optJsPath in JestFramework (see below).

It's simple to use:

Write dom test:

import org.scalajs.dom

object MyTest extends sjest.JestSuite {
  test("this is a failed test") {
    expect(1 + 1).toBe(5)

  test("dom test") {
    val div = dom.document.createElement("div")
    val body = dom.document.body.appendChild(div)
    val found = dom.document.getElementById("my-id-is-app")

Write test with shared local variable:

object MyTestWithSharedVariable extends sjest.JestSuite{
  private var marker: Int = 0

  beforeEach {
    marker += 1
  describe("outer1") {
    describe("inner2") {
      test("test2-1") {
        marker += 1
        println("do some test2-1!")
    test("test2-3") {
      marker += 1
      println("do some test2-3!")
  afterAll {
    println(marker) //4
    //Note: assertion here is useless, error here simply gets ignored by jest.

Then sbt test or testOnly like you do in any other scala test framework.

You can pass jest configs directly from console:

test -- --bail --verbose

More config:

Configs in JestFramework

class JestFramework {
  /** *opt.js full path or path relative to sbt root dir. This is prior to args */
  protected def optJsPath: String = ""
  /** Generated *.test.js full path or path relative to sbt root dir. */
  protected def testJsDir: String = "./target/scala-jests/"

  /** Yield test command, given a test.js file path. Jest configs can be put here. */
  protected def nodejsCmd(jsTestPath: String): NodejsCmd = (jsTestPath: String) =>
     NodejsCmd("node_modules/jest/bin/jest.js", js.Array("--colors", "--bail", jsTestPath))
  /** Filter jest output in sbt console */
  protected def jestOutputFilter: String => String = defaultFilter

Arguments configs:

  • -opt.js.path:<path>: *opt.js full path or path relative to sbt root dir. This will be overridden if optJsPath in JestFramework has been specified.

  • -disableAutoRunTestInSbt(default true): Whether to run actual test by 'sbt test'. 'jest xx.test.js' is executed for every test, thus worse performance. One could disable it by set this to false, and manually run jest from command line.

  • -silentOnPass (default false): Whether to suppress console output when test suite passes.

these will be stripped from arguments before passed to jest

Global life cycle:

How sjest works?

Scala-jest exposes client tests in *opt.js, and generates *.test.js files to call them, executed by nodejs' child_process, which then triggers jest. So scala.js is not involved the when testing is running, only the stdout/err shown in sbt console.

A problem is how to share objects/instances between these processes? Like:

object Global{
  var shared_in_multiple_TestSuites = ??? //not working...

The Global object is in limit scope as every test suite is executed in its own process. Unfortunately, jesting all *.test.js at once is not working too.

Global state

Communication between sub-processes is used to realize inter-test-suite sharing(not implemented yet). This also brings the ability to do global setup/teardown.

class JestFramework {
  /** Setup before run */
  protected def beforeGlobal(): Any = ()
  /** Teardown after run */
  protected def afterGlobal(stub: Any): Any = stub

The result returned from beforeGlobal will be passed as a stub to afterGlobal.


  1. Dom not exists until run in jest, that means access of dom outside test block will get NullPointerException. Use def or lazy val to overcome this problem:
object MyTest extends sjest.JestSuite{
  lazy val div = dom.document.createElement("div")
  test("dom test"){...access div here}


Jest facade is from scalajs-jest

Author: Cause Chung ([email protected])

License: Apache License Version 2.0