olafurpg / munit   0.1.4


Scala testing library with inspirations from JUnit, ScalaTest, utest and ava

Scala versions: 2.13 2.12 2.11


FunSuite is a Scala testing library with the following goals:

  • Reuse JUnit: FunSuite is implemented as a JUnit runner and tries to build on top of existing JUnit functionality where possible. Any tool that knows how to run a JUnit test suite knows how to run FunSuite, including IDEs like IntelliJ.
  • Helpful console output: test reports are pretty-printed with colors to help you quickly understand what caused a test failure. FunSuite tries to displays diffs and source locations when possible and it does a best-effort to highlight relevant stack trace elements.
  • No Scala dependencies: FunSuite is¬†implemented in ~1k lines of Scala code with no external Scala dependencies. The transitive Java dependencies weigh in total ~500kb, which is mostly¬†just JUnit.

Table of contents

Getting started

Badge with version of the latest release

// Published for 2.11, 2.12 and 2.13. JVM-only.
libraryDependencies += "com.geirsson" %% "funsuite" % "VERSION"
testFrameworks += new TestFramework("funsuite.Framework")

Next, write a test suite.

class MySuite extends funsuite.FunSuite {
  test("hello") {
    val obtained = 42
    val expected = 43
    assertEquals(obtained, expected)


Source locations for assertion errors

Assertion errors show the source code location where the assertion failed. Use cmd+click on the location "/path/to/BasicSuite.scala:36" to open the exact line number in your editor (may not work in all terminals).

Source locations for assertion errors

Highlighted stack traces

Stack frame elements for classes that are defined in your project sources are highlighted so you can focus on the important parts of the stack trace.

Highlighted stack traces example

Multiline string diff

Use assertNoDiff(obtained, expected) to compare large multi-line strings.

Multiline string diff

Test failures include the obtained multiline string in a copy-paste friendly format making it easy to update the test as the expected behavior of your program changes.


Running logic before and after tests

Override beforeAll(), beforeEach(), afterAll() and afterEach() to add custom logic that should run before and after tests run. For example, use this feature to create temporary files before executing tests or clean up acquired resources after the test finish.

class MySuite extends funsuite.FunSuite {
  // Runs once before all tests start.
  override def beforeAll(context: BeforeAll): Unit = ???
  // Runs before each individual test.
  override def beforeEach(context: BeforeEach): Unit = ???
  // Runs after each individual test.
  override def afterEach(context: AfterEach): Unit = ???
  // Runs once after all tests have completed.
  override def afterAll(context: AfterAll): Unit = ???

Skip test based on dynamic conditions

Use assume(condition, explanation) to skip tests when some conditions do not hold. For example, use assume to conditionally run tests based on the operating system or the Scala compiler version.

import scala.util.Properties
  test("paths") {
    assume(Properties.isLinux, "this test runs only on Linux")
    assume(Properties.versionNumberString.startsWith("2.13"), "this test runs only on Scala 2.13")

Tag flaky tests

Use .flaky to mark a test case that has a tendendency to fail sometimes.

  test("requests".flaky) {
    // I/O heavy tests that sometimes fail

By default, flaky tests fail unless the FUNSUITE_FLAKY_OK environment variable is set to true. Override the isFlakyFailureOk method to customize when it's OK for flaky tests to fail.

Failing tests

Use .fail to mark a test case that is expected to fail.

  test("issue-456".fail) {
    // Reproduce reported bug

A failed test only succeeds if the test body fails. If the test body succeeds, the test fails.

Running individual test

Use .only to run only a single test.

  test("issue-457") {
    // will not run
  test("issue-456".only) {
    // only test that runs
  test("issue-455") {
    // will not run

Use testOnly -- $GLOB to filter a fully qualified test name from the command line.

# sbt shell
> testOnly -- *issue-456

Use testOnly -- --only=$TEST_FILTER to filter an individual test name from the command line.

# sbt shell
> testOnly -- --only=issue-456

Ignore tests

Use the @Ignore annotation to skip all tests in a test suite.

class MySuite extends funsuite.FunSuite {
  test("hello1") {
    // will not run
  test("hello2") {
    // will not run
  // ...

Use .ignore to skip an individual test case in a test suite.

  test("issue-456".ignore) {
    // will not run

Using JUnit categories

Use @Category(...) to group tests suites together.

package myapp
import org.junit.experimental.categories.Category

class Slow extends funsuite.Tag("Slow")
class Fast extends funsuite.Tag("Fast")

class MySlowSuite extends funsuite.FunSuite {
  test("slow") {
  // ...
@Category(Array(classOf[Slow], classOf[Fast]))
class MySlowFastSuite extends funsuite.FunSuite {
  // ...
class MyFastSuite extends funsuite.FunSuite {
  // ...

Next, use --include-category=$CATEGORY and --exclude-category=$CATEGORY to determine what test suites to run from the command line.

# matches: MySlowSuite, MySlowFastSuite
> testOnly -- --include-category=myapp.Slow

# matches: MySlowSuite
> testOnly -- --include-category=myapp.Slow --exclude-category=myapp.Fast

Searching for failed tests in large log files

Test results are formatted in a specific way to make it easy to search for them in a large log file.

Test Prefix
Failed ==> X
Ignored ==> i
Success ==> +
Skipped ==> s

Knowing these prefixes may come in handy for example when browsing test logs in a browser. Search for "==> X" to quickly navigate to the failed tests.

Running tests in IntelliJ

FunSuite test suites run in IntelliJ like normal.

Running FunSuite from IntelliJ

It's expected that it's not possible to run individual test cases from IntelliJ since it does not understand the structure of the test("name") {...} syntax. As a workaround, use the .only marker to run only a single test from IntelliJ.

- test("name") {
+ test("name".only) {
    // ...

Tests as values

FunSuite test cases are represented with the type funsuite.Test and can be manipulated as a normal data structure. Feel free to tweak and extend how you generate funsuite.Test to suit your needs.

Extend Suit

Extend the base class funsuite.Suite to customize exactly what Seq[Test] you want to run.

class MyCustomSuite extends funsuite.Suite {
  // The type returned by bodies of test cases.
  // Is defined as `Any` in `funsuite.FunSuite` but it's abstract in `funsuite.Suite`
  override type TestValue = Future[String]
  override def funsuiteTests() = List(
    new Test(
      // compile error if it's not a Future[String]
      body = () => Future.successful("Hello world!"),
      tags = Set.empty[Tag],
      location = Location.generate

The abstract funsuite.Suite class only includes the before/after APIs and not other methods like assert or test().

Customize evaluation of tests

Override funsuiteRunTest() to extend the default behavior for how test bodies are evaluated. For example, use this feature to implement a Rerun(N) modifier to evaluate the body multiple times.

import scala.util.Properties
case class Rerun(count: Int) extends Tag("Rerun")
class MyWindowsSuite extends funsuite.FunSuite {
  override def funsuiteRunTest(options: TestOptions, body: => Any): Any = {
    val rerunCount = options.tags.collectFirst {
      case Rerun(n) => n
    1.to(rerunCount).map(_ => super.funsuiteRunTest(options, body))
  test("files", Rerun(10)) {
    println("Hello") // will run 10 times
  test("files") {
    // will run once, like normal

Filter tests based on dynamic conditions

Override funsuiteTests() to customize what tests get executed. For example, use this feature to skip tests based on a dynamic condition.

import scala.util.Properties
case object Windows extends funsuite.Tag("Windows")
class MyWindowsSuite extends funsuite.FunSuite {
  override def funsuiteTests(): Any = {
    val default = super.funsuiteTests()
    if (!Properties.isWin) default
    else default.filter(_.tags.contains(Windows))
  test("files", Windows) {
    // will only run in Windows
  test("files") {
    // will run like normal


JVM-only: FunSuite is currently only published for the JVM. FunSuite uses a JUnit testing interface for sbt that's written in Java so that would need to be changed in order to add Scala.js and Scala Native support. Feel free to open an issue if you would like to contribute cross-platform support.


FunSuite is inspired by several existing testing libraries:

  • ScalaTest: the syntax for defining FunSuite test suites is the same as for org.scalatest.FunSuite.
  • JUnit: FunSuite is implemented as a custom JUnit runner and features like assume test filters are implemented on top of existing JUnit functionality.
  • utest: the nicely formatted stack traces and test reports is heavily inspired by the beautifully formatted output in utest.
  • ava: the idea for showing the source locations for assertion errors comes from ava, a JavaScript testing library.

Do we really need another testing library?

FunSuite is built on the idea that >90% of what a JVM testing library needs is already provided by JUnit. However, the default JUnit testing syntax is based on annotations and does not feel idiomatic when used from Scala. FunSuite tries to fill in the gap by providing a small Scala API on top of JUnit.

Coming from ScalaTest

Add the following settings to run ScalaTest and JUnit suites with the same testing framework as FunSuite.

// build.sbt
testFrameworks := List(
  new TestFramework("funsuite.Framework"),
  new TestFramework("com.geirsson.junit.PantsFramework")

These settings configure all JUnit and ScalaTest suites to run with the same testing interface as FunSuite. This means that you get the same pretty-printing of test reports for JUnit, ScalaTest and FunSuite.

Next, you may want to start migrating your test suites one by one. If you only use basic ScalaTest features, you should be able to replace usage of org.scalatest.FunSuite with minimal changes like below.

- import org.scalatest.funsuite.AnyFunSuite
- import org.scalatest.FunSuite
+ import funsuite.FunSuite

- class MySuite extends FunSuite with BeforeAll with AfterAll {
+ class MySuite extends FunSuite {
  test("name") {
    // unchanged

- ignore("ignored") {
+ test("ignored".ignore) {
    // unchanged


FunSuite is a new library with no stability guarantees. It's expected that new releases, including patch releases, will have binary and source breaking changes.