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A simple testing framework for Scala

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uTest (pronounced micro-test) is a simple, intuitive testing library for Scala. Its key features are:

Unlike traditional testing libraries for Scala (like Scalatest or Specs2) uTest aims to be simple enough you will never get lost in its codebase and functionality, so you can focus on what's most important: your tests.

While uTest has many fewer features than other libraries, the features that it does provide are polished and are enough to build and maintain test suites of any size. uTest is used for countless projects, from the 1-file test suite for Fansi to the 50-file 9,000-line test suite for Ammonite


Getting Started

Most people coming to uTest will be running tests through SBT. Add the following to your build.sbt and you can immediately begin defining and running tests programmatically.

libraryDependencies += "com.lihaoyi" %% "utest" % "0.6.3" % "test"

testFrameworks += new TestFramework("utest.runner.Framework")

To use it with Scala.js or Scala-Native:

libraryDependencies += "com.lihaoyi" %%% "utest" % "0.6.3" % "test"

testFrameworks += new TestFramework("utest.runner.Framework")

For Scala-Native, you will also need

nativeLinkStubs := true

Defining and Running a Test Suite

Put this in your src/test/scala/ folder:

package test.utest.examples

import utest._

object HelloTests extends TestSuite{
  val tests = Tests{
    'test1 - {
      throw new Exception("test1")
    'test2 - {
    'test3 - {
      val a = List[Byte](1, 2)

You can then run this via

sbt myproject/test

Which should produce this output:

-------------------------------- Running Tests --------------------------------
Setting up CustomFramework
X test.utest.examples.HelloTests.test1 4ms
  java.lang.Exception: test1
+ test.utest.examples.HelloTests.test2.inner 0ms  1
X test.utest.examples.HelloTests.test3 0ms
  java.lang.IndexOutOfBoundsException: 10
Tearing down CustomFramework
Tests: 3, Passed: 1, Failed: 2

The tests are run one at a time, and any tests that fail with an exception have their stack trace printed. If the number of tests is large, a separate results-summary and failures-summary will be shown after all tests have run.

Nesting Tests

Note that tests within the suite can nested within each other, but only directly. E.g. you cannot define tests within if-statements or for-loops. uTest relies on the test structure to be statically known at compile time. They can be nested arbitrarily deep:

package test.utest.examples

import utest._

object NestedTests extends TestSuite{
  val tests =  Tests{
    val x = 1
    'outer1 - {
      val y = x + 1

      'inner1 - {
        assert(x == 1, y == 2)
        (x, y)
      'inner2 - {
        val z = y + 1
        assert(z == 3)
    'outer2 - {
      'inner3 - {
        assert(x > 1)

Here, we have a tree of nested blocks, with three tests at the inner-most blocks of this tree: innerest, inner2 and inner3. Test blocks can be nested arbitrary deeply to help keep things neat, and only the inner-most blocks are considered to be tests.

When this suite is run with sbt myproject/test, it is those three tests that get executed:

------------------------------- Running Tests -------------------------------
+ test.utest.examples.NestedTests.outer1.inner1 21ms  (1,2)
+ test.utest.examples.NestedTests.outer1.inner2 0ms
+ test.utest.examples.NestedTests.outer2.inner3 0ms 

You can see also that test.utest.examples.NestedTests.outer1.inner1 displays the value of (x, y) returned from the test: (1,2). Returning a value from a test is useful if you want to skim the test's results after a run to perform manual sanity-checks on some computed value.

If you find yourself wanting to define a test in a for, loop, e.g.

// Doesn't work!
val tests =  Tests{ 
  for(fileName <- Seq("hello", "world", "i", "am", "cow")){
    fileName - {
      // lots of code using fileName

You can instead factor out the common code into a function, and call that from each distinct test case:

// Works!
val tests = Tests{
  def runTestChecks(fileName: String) = {
    // lots of code using fileName
  "hello" - runTestChecks("hello")
  "world" - runTestChecks("world")
  "i" - runTestChecks("i")
  "am" - runTestChecks("am")
  "cow" - runTestChecks("cow")

Or even using the TestPath that is available implicitly to every test, you can remove the duplication between the test name and the call to runTestChecks():

# Also works!
val tests = Tests{
  def runTestChecks()(implicit path: utest.framework.TestPath) = {
    val fileName = path.value.last
    // lots of code using fileName
  "hello" - runTestChecks()
  "world" - runTestChecks()
  "i" - runTestChecks()
  "am" - runTestChecks()
  "cow" - runTestChecks()

Running Tests

Apart from running all tests at once using

sbt myproject/test

You can also run individual tests using their full path e.g.

sbt 'myproject/test-only -- test.utest.examples.NestedTests.outer1.inner1'
sbt 'myproject/test-only -- test.utest.examples.NestedTests.outer2.inner2'
sbt 'myproject/test-only -- test.utest.examples.NestedTests.outer2.inner3'

You can also wrap the test selector in double quotes, which lets you run test whose path segments contain spaces or other special characters:

sbt 'myproject/test-only -- "test.utest.examples.NestedTests.segment with spaces.inner"'

You can run groups of tests by providing the path to the block enclosing all of them:

# runs both tests `inner1` and `inner2`
sbt 'myproject/test-only -- test.utest.examples.NestedTests.outer1'

# runs all tests in the `NestedTests` test suite
sbt 'myproject/test-only -- test.utest.examples.NestedTests'

# runs all tests in `NestedTests` and any other suites within `test.utest.examples`
sbt 'myproject/test-only -- test.utest.examples'

You can also use the {foo,bar} syntax to specify exactly which tests you would like to run:

# runs both tests `inner2` and `inner3`, explicitly
sbt 'myproject/test-only -- test.examples.NestedTests.outer1.{inner1,inner2}'

# runs `outer1.inner1` and `outer2.inner3` but not `outer1.inner2`
sbt 'myproject/test-only -- test.examples.NestedTests.{outer1.inner1,outer2.inner3}'

# also runs `inner1` and `innerest` (and any other test inside `inner1`) but not `inner2`
sbt 'myproject/test-only -- test.examples.NestedTests.{outer1.inner1,outer2}'

The same syntax can be used to pick and choose specific TestSuites to run, or tests within those test suites:

# Run every test in `HelloTests` and `NestedTests`
sbt 'myproject/test-only -- test.examples.{HelloTests,NestedTests}'

# Runs `HelloTests.test1`, `NestedTests.outer1.inner2` and `NestedTests.outer2.inner3`
sbt 'myproject/test-only -- test.examples.{HelloTests.test1,NestedTests.outer2}'
sbt 'myproject/test-only -- {test.examples.HelloTests.test1,test.examples.NestedTests.outer2}'

In general, it doesn't really matter if you are running individual tests, groups of tests within a TestSuite, individual TestSuites, or packages containing TestSuite. These all form one a single large tree of tests that you can run, using the same uniform syntax.

By default, SBT runs multiple test suites in parallel, so the output from those suites may be interleaved. You can set parallelExecution in Test := false in your SBT config to make the tests execute sequentially, so the output from each suite will be grouped together in the terminal.

uTest defaults to emitting ANSI-colored terminal output describing the test run. You canconfigure the colors by overriding methods on your test suite, or disable it altogether with override def formatColor = false.

Sharing Setup Code, and Sharing Setup Objects

As you saw in the previous section, you can define blocks tests to group them together, and have them share common initialization code in the enclosing block. You can also define mutable values, or fixtures in the shared initialization code, and each nested test with a Tests block gets its own copy of any mutable variables defined within it:

package test.utest.examples

import utest._

object SeparateSetupTests extends TestSuite{
  val tests = Tests{
    var x = 0
    'outer1 - {
      x += 1
      'inner1 - {
        x += 2
        assert(x == 3) // += 1, += 2
      'inner2 - {
        x += 3
        assert(x == 4) // += 1, += 3
    'outer2 - {
      x += 4
      'inner3 - {
        x += 5
        assert(x == 9) // += 4, += 5

Here, you can see that the x available in each inner test block (inner1, inner2, inner3) is separate and independent: each test gets a new copy of x, modified only by that test's enclosing blocks. This helps avoid inter-test interference (where a test ends up implicitly depending on some state initialized by another test running earlier in the block) while still making it convenient to share common setup code between the various tests in your suite.

If you want the mutable fixtures to really-truly be shared between individual tests (e.g. because they are expensive to repeatedly initialize) define it outside the Tests{} block in the enclosing object:

package test.utest.examples

import utest._

object SharedFixturesTests extends TestSuite{
  var x = 0
  val tests = Tests{
    'outer1 - {
      x += 1
      'inner1 - {
        x += 2
        assert(x == 3) // += 1, += 2
      'inner2 - {
        x += 3
        assert(x == 7) // += 1, += 2, += 1, += 3
    'outer2 - {
      x += 4
      'inner3 - {
        x += 5
        assert(x == 16) // += 1, += 2, += 1, += 3, += 4, += 5

Here you see that the changes to x are being shared between the invocations of all the tests. If you are initializing something expensive to share between tests, this allows you to avoid paying that cost multiple times, but you need to be careful the tests aren't mutating shared state that could cause other tests to fail!

Other Ways of Naming tests

uTest also allows you to use strings to define test keys, if you wish to make your test names longer and more descriptive:

"test with spaces" - {
  throw new Exception("test1")

You can also use the 'symbol - ... syntax, if your tests are simply forwarding to a separate helper method to do the real testing:

'test1 - processFileAndCheckOutput("input1.txt", "expected1.txt")
'test2 - processFileAndCheckOutput("input2.txt", "expected2.txt")
'test3 - processFileAndCheckOutput("input3.txt", "expected3.txt")

The "string" - {...} and 'symbol - ... syntaxes are equivalent.

The last way of defining tests is with the utest.* symbol, e.g. these tests from the Fansi project:

'parsing - {
  def check(frag: fansi.Str) = {
    val parsed = fansi.Str(frag.render)
    assert(parsed == frag)
  * - check(fansi.Color.True(255, 0, 0)("lol"))
  * - check(fansi.Color.True(1, 234, 56)("lol"))
  * - check(fansi.Color.True(255, 255, 255)("lol"))
  * - {
    (for(i <- 0 to 255) yield check(fansi.Color.True(i,i,i)("x"))).mkString
  * - check(
    "#" + fansi.Color.True(127, 126, 0)("lol") + "omg" + fansi.Color.True(127, 126, 0)("wtf")

  * - check(square(for(i <- 0 to 255) yield fansi.Color.True(i,i,i)))

Tests defined using the * symbol are give the numerical names 0, 1, 2, etc.. This is handy if you have a very large number of very simple test cases, don't really care what each one is called, but still want to be able to run them and collect their result separately.

Asynchronous Tests

val tests = Tests {
  "testSuccess" - {
    Future {
  "testFail" - {
    Future {
  "normalSuccess" - {
  "normalFail" - {

tests.runAsync().map { results =>
  assert(results.toSeq(0).value.isSuccess) // root
  assert(results.toSeq(1).value.isSuccess) // testSuccess
  assert(results.toSeq(2).value.isFailure) // testFail
  assert(results.toSeq(3).value.isSuccess) // normalSuccess

You can have tests which return (have a last expression being) a Future[T] instead of a normal value. You can run the suite using .runAsync to return a Future of the results, or you can continue using .run which will wait for all the futures to complete before returning.

In Scala.js, calling .run on a test suite with futures in it throws an error instead of waiting, since you cannot wait for asynchronous results in Scala.js.

When running the test suites from SBT, you do not need worry about any of this run vs runAsync stuff: the test runner will handle it for you and provide the correct results.

Smart Asserts

val x = 1
val y = "2"
  x > 0,
  x == y

// utest.AssertionError: x == y
// x: Int = 1
// y: String = 2

uTest comes with a macro-powered smart asserts that provide useful debugging information in the error message. These take one or more boolean expressions, and when they fail, will print out the names, types and values of any local variables used in the expression that failed. This makes it much easier to see what's going on than Scala's default assert, which gives you the stack trace and nothing else.

uTest also wraps any exceptions thrown within the assert, to help trace what went wrong:

val x = 1L
val y = 0L
assert(x / y == 10)

// utest.AssertionError: assert(x / y == 10)
// caused by: java.lang.ArithmeticException: / by zero
// x: Long = 1
// y: Long = 0

The origin exception is stored as the cause of the utest.AssertionError, so the original stack trace is still available for you to inspect.

uTest's smart asserts live on the utest package, and are brought into scope via import utest._. If you want to continue using the built-in Scala asserts, e.g. if you want custom messages if the assert fails, those remain available as Predef.assert.

Arrow Asserts

1 ==> 1 // passes
Array(1, 2, 3) ==> Array(1, 2, 3) // passes
  1 ==> 2 // throws
}catch{case e: java.lang.AssertionError =>

You can use a ==> b as a shorthand for assert(a == b). This results in pretty code you can easily copy-paste into documentation.


val e = intercept[MatchError]{
  (0: Any) match { case _: String => }

// scala.MatchError: 0 (of class java.lang.Integer)

intercept allows you to verify that a block raises an exception. This exception is caught and returned so you can perform further validation on it, e.g. checking that the message is what you expect. If the block does not raise one, an AssertionError is raised.

As with assert, intercept adds debugging information to the error messages if the intercept fails or throws an unexpected Exception.

Eventually and Continually

val x = Seq(12)
eventually(x == Nil)

// utest.AssertionError: eventually(x == Nil)
// x: Seq[Int] = List(12)

In addition to a macro-powered assert, uTest also provides macro-powered versions of eventually and continually. These are used to test asynchronous concurrent operations:

  • eventually(tests: Boolean*): ensure that the boolean values of tests all become true at least once within a certain period of time.
  • continually(tests: Boolean*): ensure that the boolean values of tests all remain true and never become false within a certain period of time.

These are implemented via a retry-loop, with a default retry interval of 0.1 second and retries up to a total of 1 second. If you want to change this behavior, you can shadow the implicit values retryInterval and retryMax, for example this:

implicit val retryMax = RetryMax(300.millis)
implicit val retryInterval = RetryInterval(50.millis)

Would set the retry-loop to happen every 50ms up to a max of 300ms.

Together, these two operations allow you to easily test asynchronous operations. You can use them to help verify Liveness properties (that condition must eventually be met) and Safety properties (that a condition is never met)

As with assert, eventually and continually add debugging information to the error messages if they fail.

Assert Match

assertMatch(Seq(1, 2, 3)){case Seq(1, 2) =>}
// AssertionError: Matching failed Seq(1, 2, 3)

assertMatch is a convenient way of checking that a value matches a particular shape, using Scala's pattern matching syntax. This includes support for use of | or _ or if-guards within the pattern match. This gives you additional flexibility over a traditional assert(a == Seq(1, 2)), as you can use _ as a wildcard e.g. using assertMatch(a){case Seq(1, _)=>} to match any 2-item Seq whose first item is 1.

As with assert, assertMatch adds debugging information to the error messages if the value fails to match or throws an unexpected Exception while evaluating.

Compile Error

compileError("true * false")
// CompileError.Type("value * is not a member of Boolean")

// CompileError.Parse("')' expected but '}' found.")

compileError is a macro that can be used to assert that a fragment of code (given as a literal String) fails to compile.

  • If the code compiles successfully, compileError will fail the compilation run with a message.
  • If the code fails to compile, compileError will return an instance of CompileError, one of CompileError.Type(pos: String, msgs: String*) or CompileError.Parse(pos: String, msgs: String*) to represent typechecker errors or parser errors

In general, compileError works similarly to intercept, except it does its checks (that a snippet of code fails) and errors (if it doesn't fail) at compile-time rather than run-time. If the code fails as expected, the failure message is propagated to runtime in the form of a CompileError object. You can then do whatever additional checks you want on the failure message, such as verifying that the failure message contains some string you expect to be there.

The compileError macro compiles the given string in the local scope and context. This means that you can refer to variables in the enclosing scope, i.e. the following example will fail to compile because the variable x exists.

val x = 0

compileError("x + x"),
// [error] compileError check failed to have a compilation error

The returned CompileError object also has a handy .check method, which takes a position-string indicating where the error is expected to occur, as well as zero-or-more messages which are expected to be part of the final error message. This is used as follows:

compileError("true * false").check(
compileError("true * false").check(
  "value * is not a member of Boolean"

Note that the position-string needs to exactly match the line of code the compile-error occured on. This includes any whitespace on the left, as well as any unrelated code or comments sharing the same line as the compileError expression.

Test Utilities

uTest provides a range of test utilities that aren't strictly necessary, but aim to make your writing of tests much more convenient and DRY.


package test.utest.examples

import utest._

object TestPathTests extends TestSuite{
  val tests = Tests{
      'foo {
        assert(implicitly[utest.framework.TestPath].value == Seq("testPath", "foo"))

uTest exposes the path to the current test to the body of the test via the utest.framework.TestPath implicit. This can be used to print debugging information while the test is running (test 50% done) or to avoid repetition between the test name and test body.

One example is the Fastparse test suite, which uses the name of the test to provide the repository that it needs to clone and parse:

def checkRepo(filter: String => Boolean = _ => true)
             (implicit testPath: utest.framework.TestPath) = {
  val url = "" + testPath.value.last
  import sys.process._
  val name = url.split("/").last
  if (!Files.exists(Paths.get("target", "repos", name))){
    Seq("git", "clone", url, "target/repos/"+name, "--depth", "1").!
  checkDir("target/repos/"+name, filter)

"lihaoyi/fastparse" - checkRepo()
"scala-js/scala-js" - checkRepo()
"scalaz/scalaz" - checkRepo()
"milessabin/shapeless" - checkRepo()
"akka/akka"- checkRepo()
"lift/framework" - checkRepo()
"playframework/playframework" - checkRepo()
"PredictionIO/PredictionIO" - checkRepo()
"apache/spark" - checkRepo()

This allows us to keep the tests DRY - avoiding having to repeat the name of the repo in the name of the test for every test we define - as well as ensuring that they always stay in sync.

If you need additional metadata such as line-numbers or file-paths or class or package names, you can use the SourceCode library's implicits to pull them in for you.

Local Retries

object LocalRetryTests extends utest.TestSuite{
  val flaky = new FlakyThing
  def tests = Tests{
    'hello - retry(3){

You can wrap individual tests, or even individual expressions, in a retry block to make them retry a number of times before failing. That is very useful for dealing with small points of flakiness within your test suite. A retry block simply retries its body up to the specified number of times; the first run that doesn't throw an exception returns the value returned by that run.

You can also use Suite Retries if you want to configure retries more globally across your test suite.

Configuring uTest

Per-Run Setup/Teardown, and other test-running Config

To configure things which affect an entire test run, and not any individual TestSuite object, you can create your own subclass of utest.runner.Framework and override the relevant methods.

For example, if you need to perform some action (initialize a database, cleanup the filesystem, etc.) not just per-test but per-run, you can do that by defining a custom utest.runner.Framework and overriding the setup and teardown methods:

class CustomFramework extends utest.runner.Framework{
  override def setup() = {
    println("Setting up CustomFramework")
  override def teardown() = {
    println("Tearing down CustomFramework")

And then telling SBT to run tests using the custom framework:

testFrameworks += new TestFramework("test.utest.CustomFramework"),

This is handy for setup/teardown that is necessary but too expensive to do before/after every single test, which would be the case if you used Test Wrapping to do it.

Apart from setup and teardown, there are other methods on utest.runner.Framework that you can override to customize:

    * Override to run code before tests start running. Useful for setting up
    * global databases, initializing caches, etc.
  def setup() = ()

    * Override to run code after tests finish running. Useful for shutting
    * down daemon processes, closing network connections, etc.
  def teardown() = ()

    * How many tests need to run before uTest starts printing out the test
    * results summary and test failure summary at the end of a test run. For
    * small sets of tests, these aren't necessary since all the output fits
    * nicely on one screen; only when the number of tests gets large and their
    * output gets noisy does it become valuable to show the clean summaries at
    * the end of the test run.
  def showSummaryThreshold = 30

    * Whether to use SBT's test-logging infrastructure, or just println.
    * Defaults to println because SBT's test logging doesn't seem to give us
    * anything that we want, and does annoying things like making a left-hand
    * gutter and buffering input by default
  def useSbtLoggers = false

  def resultsHeader = BaseRunner.renderBanner("Results")
  def failureHeader = BaseRunner.renderBanner("Failures")

  def startHeader(path: String) = BaseRunner.renderBanner("Running Tests" + path)

Output Formatting

You can control how the output of tests gets printed via overriding methods on the Framework class, described above. For example, this snippet overrides the exceptionStackFrameHighlighter method to select which stack frames in a stack trace are more relevant to you, so they can be rendered more brightly:

class CustomFramework extends utest.runner.Framework{
  override def exceptionStackFrameHighlighter(s: StackTraceElement) = {

This results in stack traces being rendered as such:


the utest.runner.Framework provides a wide range of hooks you can use to customize how the uTest output is colored, wrapped, truncated or formatted:

def formatColor: Boolean = true
def formatTruncateHeight: Int = 15
def formatWrapWidth: Int = 100

def formatValue(x: Any) = testValueColor(x.toString)

def toggledColor(t: ufansi.Attrs) = if(formatColor) t else ufansi.Attrs.Empty
def testValueColor = toggledColor(ufansi.Color.Blue)
def exceptionClassColor = toggledColor(ufansi.Underlined.On ++ ufansi.Color.LightRed)
def exceptionMsgColor = toggledColor(ufansi.Color.LightRed)
def exceptionPrefixColor = toggledColor(ufansi.Color.Red)
def exceptionMethodColor = toggledColor(ufansi.Color.LightRed)
def exceptionPunctuationColor = toggledColor(ufansi.Color.Red)
def exceptionLineNumberColor = toggledColor(ufansi.Color.LightRed)
def exceptionStackFrameHighlighter(s: StackTraceElement) = true

def formatResultColor(success: Boolean) = toggledColor(
  if (success) ufansi.Color.Green
  else ufansi.Color.Red

def formatMillisColor = toggledColor(ufansi.Bold.Faint)

Any methods overriden on your own custom Framework apply to every TestSuite that is run. If you want to further customize how a single TestSuite's output is formatted, you can override utestFormatter on that test suite.

Note that uTest uses an internal copy of the Fansi library, vendored at utest.ufansi, in order to avoid any compatibility problems with any of your other dependencies. You can use ufansi to construct the colored ufansi.Strs that these methods require, or you could just return colored java.lang.String objects containing ANSI escapes, created however you like, and they will be automatically parsed into the correct format.

Suite Retries

You can mix in the TestSuite.Retries trait to any TestSuite and define the utestRetryCount int to enable test-level retries for all tests within a suite:

object SuiteRetryTests extends TestSuite with TestSuite.Retries{
  override val utestRetryCount = 3
  val flaky = new FlakyThing
  def tests = Tests{

You can also use Local Retries if you want to only retry within specific tests or expressions instead of throughout the entire suite.

Running code before and after test cases

uTest offers the utestBeforeEach and utestAfterEach methods that you can override on any TestSuite, these methods are invoked before and after running each test.

def utestBeforeEach(path: Seq[String]): Unit = ()
def utestAfterEach(path: Seq[String]): Unit = ()

These are equivalent to utestWrap but easier to use for simple cases.

package test.utest.examples

import utest._
object BeforeAfterEachTest extends TestSuite {
  var x = 0
  override def utestBeforeEach(): Unit = {
    println(s"on before each x: $x")
    x = 0
  override def utestAfterEach(): Unit =
    println(s"on after each x: $x")

  val tests = Tests{
    'outer1 - {
      x += 1
      'inner1 - {
        x += 2
        assert(x == 3) // += 1, += 2
      'inner2 - {
        x += 3
        assert(x == 4) // += 1, += 3
    'outer2 - {
      x += 4
      'inner3 - {
        x += 5
        assert(x == 9) // += 4, += 5
-------------------------------- Running Tests --------------------------------
Setting up CustomFramework
on before each x: 0
on after each x: 3
+ test.utest.examples.BeforeAfterEachTest.outer1.inner1 22ms  3
on before each x: 3
on after each x: 4
+ test.utest.examples.BeforeAfterEachTest.outer1.inner2 1ms  4
on before each x: 4
on after each x: 9
+ test.utest.examples.BeforeAfterEachTest.outer2.inner3 0ms  9
Tearing down CustomFramework
Tests: 3, Passed: 3, Failed: 0

Both utestBeforeEach and utestAfterEach runs inside utestWrap's body callback.

If you need something fancier than what utestBeforeEach or utestAfterEach provide, e.g. passing initialized objects into the main test case or tearing them down after the test case has completed, feel free to define your test wrapper/initialization function and use it for each test case:

def myTest[T](func: Int => T) = {
  val fixture = 1337 // initialize some value 
  val res = func(fixture) // make the value available in the test case
  assert(fixture == 1337) // properly teardown the value later

'test - myTest{ fixture =>
  // do stuff with fixture

The above myTest function can also take a TestPath implicit if it wants access to the current test's path.

Running code before and after test suites

If you're looking for something like utestBeforeAll, you can add your code to the object body, and you can also use lazy val to delay the initialization until the test suite object is created.

uTest offers the utestAfterAll method that you can override on any test suite, this method is invoked after running the entire test suite.

def utestAfterAll(): Unit = ()
package test.utest.examples

import utest._
object BeforeAfterAllSimpleTests extends TestSuite {
  println("on object body, aka: before all")

  override def utestAfterAll(): Unit = {
    println("on after all")

  val tests = Tests {
    'outer1 - {
      'inner1 - {
      'inner2 - {

-------------------------------- Running Tests --------------------------------
Setting up CustomFramework
on object body, aka: before all
+ test.utest.examples.BeforeAfterAllSimpleTests.outer1.inner1 2ms  1
+ test.utest.examples.BeforeAfterAllSimpleTests.outer1.inner2 0ms  2
on after all

Test Wrapping

uTest exposes the utestWrap function that you can override on any test suite:

def utestWrap(path: Seq[String], runBody: => concurrent.Future[Any])
             (implicit ec: ExecutionContext): concurrent.Future[Any]

This is a flexible function that wraps every test call; you can use it to:

  • Perform initialization before evaluating runBody
  • Perform cleanup after the completion of runBody via runBody.onComplete
  • Perform retries by executing runBody multiple times
  • Log the start and end times of each test, along with the path of that test, e.g. Seq("outer", "inner1", "innerest") for the test outer.inner1.innerest

Generally, if you want to perform messy before/after logic around every individual test, override utestWrap. Please remember to call the utestBeforeEach and utestAfterEach methods when needed.

runBody is a future to support asynchronous testing, which is the only way to test things like Ajax calls in Scala.js

Scala.js and Scala-Native

uTest is completely compatible with Scala.js and Scala-Native: the above sections on defining a test suite, asserts and the test-running API all work unchanged under ScalaJS, with minor differences:

  • ScalaJS does not support parallelism, and as such only single-threaded ExecutionContexts like utest.ExecutionContext.runNow or scala.scalajs.concurrent.JSExecutionContext.runNow work. When run via SBT, --parallel has no effect.
  • Eventually and Continually are not supported, as they rely on a blocking retry-loop whereas you can't block in ScalaJS.

Apart from these differences, there should be no problem compiling uTest TestSuites via Scala.js and running them on Node.js, in the browser, or (with Scala-Native) on LLVM.

Note that Scala-Native support, like Scala-Native, is experimental. While it is tested in a few projects (uTest's own test suite runs in Scala-Native), it does have it's own quirks (e.g. NullPointerExceptions appear to be fatal) and does not have the weight of third-party usage that the Scala-JVM and Scala.js versions of uTest have.

Running uTest Standalone

uTest exposes a straightforward API that allows you to run tests, receive results and format them in a nice way when used standalone, without using SBT's test integration. The following code snippet demonstrates how to define tests and run them directly:

import utest._
val tests = Tests{
  'test1 - {
    // throw new Exception("test1")
  'test2 - {
    'inner - {
  'test3 - {
    val a = List[Byte](1, 2)
    // a(10)

// Run and return results
val results1 =

The call can be customized with additional arguments to control how the code is run, or can be replaced with .runAsync to handle asynchronous testing, or .runAndPrint/.runAndPrintAsync if you want to print the results of tests as they complete using the normal output formatter:

// Run, return results, and print streaming output with the default formatter
val results2 = TestRunner.runAndPrint(
// Run, return results, and print output with custom formatter and executor
val results3 = TestRunner.runAndPrint(
  executor = new utest.framework.Executor{
    override def utestWrap(path: Seq[String], runBody: => Future[Any])
                 (implicit ec: ExecutionContext): Future[Any] = {
      println("Getting ready to run " + path.mkString("."))
      runBody.andThen {
        case _ => utestAfterEach()
  formatter = new utest.framework.Formatter{
    override def formatColor = false

Lastly, you can also run TestSuite objects in the same way:

// Run `TestSuite` object directly without using SBT, and use 
// its configuration for execution and output formatting
object MyTestSuite extends TestSuite{
  val tests = Tests{
    'test1 - {
      // throw new Exception("test1")
    'test2 - {
      'inner - {
    'test3 - {
      val a = List[Byte](1, 2)
      // a(10)

val results4 = TestRunner.runAndPrint(
  executor = MyTestSuite,
  formatter = MyTestSuite

uTest provides helpers to render the standard summary reports at the end of a test run, once all your results are in:

// Show summary and exit
val (summary, successes, failures) = TestRunner.renderResults(
    "MySuiteA" -> results1,
    "MySuiteA" -> results2,
    "MySuiteA" -> results3,
    "MySuiteB" -> results4
if (failures > 0) sys.exit(1)

You can thus use uTest anywhere you can run Scala code, even when not using SBT: in a normal main method, within Ammonite scripts, or elsewhere.

Why uTest

uTest aims to give you the things that everyone needs to run tests, giving you one obvious way to do common tasks while testing. uTest is simple and compact, letting you avoid thinking about it so you can focus on what's most important: you tests.

Hence uTest provides:

uTest tries to provide things that every developer needs, in their minimal, essential form. It intentionally avoids redundant/unnecessary features or syntaxes that bloat the library and make it harder to developers to pick up, which I find to be common in other popular testing libraries like Scalatest or Specs2:

While uTest has and will continue to slowly grow and add more features, it is unlikely that it will ever reach the same level of complexity that other testing libraries are currently at.



  • Returning null from a test case no longer blows up
  • Added `utest.runner.MillFramework


  • Added support for Scala.js 1.0.0-M2.


  • Fix cross-publishing for Scala.js, which was borked in 0.6.0
  • Ensure utestAfterEach be executed regardless of a test failure


  • Migrate formatting-related configuration options from utest.TestSuite onto the utest.runner.Framework, as described here.

  • Added the exceptionStackFrameHighlighter formatting hook, letting you choose which stack frames in an exception are of interest to you so they can be rendered more brightly.



  • Cross-publish for Scala 2.13.0-M2, Scala.js 0.6.20, Scala-Native 0.3.3

  • Stack traces for chained exceptions (i.e. those with a .getCause != null) are now properly displayed when tests fail

  • Portions of stack traces caused by the internals of the assert macros are now hidden, since they aren't relevant to any failure in user code

  • Revamped test output format, motivated by drhumlen's PR 113, which should be much easier to read and skim

  • Much smarter test-output-value truncation, now based on lines-of-output (including wrapping) rather than number-of-characters

  • Line-wrapping of output is now indentation aware: it wraps to the next line with the same indentation, preserving the outline of indentation on the left making it easier to skim

  • How long tests take (im milliseconds) is now displayed in the standard test output format

  • Hierarchical test summary and failure-summary are now only shown when you have a large number of tests, since it's not use when running individual or small numbers of tests. The default threshold is 20, which can be configured by defining a custom framework overriding showSummaryThreshold

  • Revamped test-query system, now allowing you to run multiple groups of tests at once via test-only -- mypackage.{foo,bar,baz} or {mypackage, myotherpackage} or mypackage.{foo,bar.{baz,qux}}

  • Overhauled the execution model of test suites: now only the inner-most blocks within your TestSuite{...} block count as tests, and the surrounding blocks do not. Thus the surrounding blocks no longer show pass/fail status, return a test result-value, or get run independently.

  • Various user errors (non-existent test, non-existing test suite, invalid test query syntax) now give slightly more friendly error messages

  • Using uTest with fork in Test := true in SBT no longer gives an incorrect results summmary

  • Fix problem with lazy vals in test blocks crashing the compiler #67. Note that the issue is only fixed on 2.12.3, and not on Scala 2.10.x or 2.11.x.

  • Deprecated the 'foo{...} syntax for defining tests. We should standardize on "foo" - {...} or 'foo - {...}

  • The TestSuite{...} for defining a block of tests is now deprecated; it never actually defined a TestSuite object, so the name was pretty misleading. The new syntax is Tests{...}

  • Remove the MultipleErrors wrapper when you test more than one expression in an assert and multiple of them fail. Now only the first expression in the assert call which fails will have it's exception thrown.

  • Moved smart asserts from being embedded into the TestSuite objects directly onto the utest package, so they are pulled in by the import utest._ import.


  • Scala Native support.


  • Scala 2.13 support
  • Compile for Scala 2.12 with method optimisations (-opt:l:method)


  • Upgrade Scala.JS to 0.6.16.
  • Upgrade Scala to 2.11.11 and 2.12.2.
  • Avoid using getStackTraceString deprecated in Scala 2.13


  • Catch Fatal exceptions like ClassCasts in Scala.JS.


  • Scala 2.12 support



  • Move errors into utest.* from utest.framework.*
  • Removed acyclic hack variable


  • Fix usage of by-name function calls within tests #55


  • foo: @Show annotation lets you tell uTest to print out arbitrary expressions within the test suite when things fail, in addition to the default of local variables

  • You can use a ==> b to assert equality within a test suite, in a form that's pretty enough to use as documentation

  • compileError now properly passes when an expression would fail to compile due to @compileTimeOnly annotations

  • Configuring uTest has been overhauled.

  • Scala 2.12.0-M3 support

  • Fix some warnings appearing when the -Ydead-code flag is used

  • Added TestPath implicit to make the path to the current test available for usage inside the test body or helpers.


  • Published for Scala.js 0.6.1


  • Published for Scala.js 0.6.0
  • Removed JsCrossBuild now that Scala.js supports cross-building via crossProject
  • compileTimeOnly has been re-introduced, so invalid use of test DSL should fail with nice errors
  • Removed --throw flag in favor of native SBT error reporting


  • Added support for asynchronous tests which return a Future.


  • Updated to work against ScalaJS 0.5.4


  • Introduced CompileError.check(pos: String, msgs: String*) to simplify the common pattern of checking that the error occurs in the right place and with the message you expect.
  • Changed the file layout expected by JsCrossBuild, to expect the shared files to be in js/shared/ and jvm/shared/, rather than in shared/. This is typically achieved via symlinks, and should make the cross-build play much more nicely with IDEs.


  • Fix bug in utestJsSettings pulling in the wrong version of uTest


  • Introduced the compileError macro to allow testing of compilation errors.
  • Stack traces are now only shown for the user code, with the uTest/SBT internal stack trace ignored, making them much less spammy and noisy.
  • Introduced the * symbol, which can be used in place of a test name to get sequentially numbered test names.


  • ScalaJS version is now built against ScalaJS 0.5.3
  • Fixed linking errors in ScalaJS version, to allow proper operation of the new optimization


  • Fixed bug causing local-defs in assert macro to fail


  • Extracted out utestJvmSettings and utestJsSettings for use outside the JsCrossBuild plugin, for people who don't want to use the plugin.


  • Print paths of failing tests after completion to make C&P-ing re-runs more convenient
utest open issues Ask a question     (View All Issues)
  • over 3 years Better support for running single test
  • over 3 years Support running tests without sbt
  • over 3 years Show exception cause stack trace
  • over 3 years AddConvinientBeforeAndAfter
  • over 3 years customisable pretty-printing
  • almost 4 years Allow for additional output it assert
  • almost 4 years UndefinedBehaviorError uncaught; freeze SBT
  • almost 4 years Expose SBT Test Args to tests in the TestSuite
  • over 4 years allowing sbt eclipse import
  • over 4 years Default parameters are not handled well in test macros
  • almost 5 years Compiler crash caused by an edge case in TestSuite
  • almost 5 years Test reports (XML) have test cases that have empty names
  • almost 5 years 2.10: Compiler crashes when using `compileError`: SOMETHING WENT WRONG LOLS scala.reflect.internal.FatalError
  • almost 5 years lazy vals crash compiler
  • almost 5 years Exception when running testsuite from Intellij IDEA
  • almost 5 years No sure if is a problem with utest
  • almost 5 years Stack traces aren't being cutoff
  • about 5 years Changes for SJS 0.6.0?
  • about 5 years Intercept doesn't work with variable assignments
  • over 5 years Add support for Custom test configuration
  • over 5 years Only show the output/error-log-spam once when running a single test.
  • over 5 years print matched value for assertMatch
  • over 5 years wrong "Results" summary for "fork:=true"
  • almost 6 years Allow ? in addition to - for tests that must be explicitly invoked
utest open pull requests (View All Pulls)
  • Add 2.12.0-M4 version
  • fix build setting
  • DO NOT MERGE - Topic/slowest
  • Handle Fatal exceptions so SBT doesn't freeze
  • cross compile with Scala 2.12.x
  • Catch Fatal errors - should fix #89
  • Update version in readme - getting started
  • [WIP] Change presentation of test results
  • eta expand explicitly (for Scala 2.13 compatibility)
  • update version in README
  • fix typo. s/String/Symbol/
  • scala-js 0.6.22
  • upgrade scala.js to 1.0.0-M3
  • Synchronize calls to eventHandler.handle
utest questions on Stackoverflow (View All Questions)
  • How to test objects or other single resources / disable parallel testing with uTest
  • How to get the name of the current scalajs / uTest test case
  • cannot get uTest to run tests
  • sbt play cross build project setup: uTest runner doesn't seperate client/server projects correctly
  • Cannot get uTest to see my tests
  • How to fake HttpContext.Current for UTest?
utest list of languages used
utest latest release notes
v0.6.3 utest v0.6.3
  • #137 Add support for Scala.js 1.0.0-M2, by @sjrd
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