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A small Scala library for writing specs as simple classes and methods.


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No seriously, keep it simple.

simplespec is a thin Scala wrapper over JUnit, the most commonly-used test framework on the JVM. simplespec was originally written by Coda Hale and is now maintained and developed by Simple. The library features extensible Hamcrest matchers, easy mocks, and other niceties.


  • Scala 2.9.1
  • JUnit 4.10.x
  • Mockito 1.9.x

Getting Started

First, specify simplespec as a dependency:


Second, write a spec:

import com.example.Stack
import org.junit.Test
import com.simple.simplespec.Spec

class StackSpec extends Spec {
  class `An empty stack` {
    val stack = Stack()

    @Test def `has a size of zero` = {

    @Test def `is empty` = {

    class `with an item added to it` {
      stack += "woo"

      @Test def `might have an item in it` = {

Execution Model

The execution model for a Spec is just a logical extension of how JUnit itself works -- a Spec class contains one or more regular classes, each of which can contain zero or more @Test-annotated methods or further nested classes.

When JUnit runs the Spec class, it creates new instances of each class for each test method run, allowing for full test isolation. In the above example, first an instance of StackSpec would be created, then an instance of StackSpec#`An empty stack`, then an instance of StackSpec#`An empty stack`#`with an item added to it`, and finally its `might have an item in it` method is run as a test.

The tradeoff of this execution model (vs. one which shares state between test invocation) is that tests which create a substantial amount of shared state (e.g., data-intensive tests) spend a lot of time setting up or tearing down state.

Unlike JUnit, simplespec doesn't require your test methods to return void.

The outer Spec instance has beforeEach and afterEach methods which can be overridden to perform setup and teardown tasks for each test contained in the context. simplespec also provides BeforeEach, AfterEach, and BeforeAndAfterEach traits which inner classes can extend to perform more tightly-scoped setup and teardown tasks.


simplespec provides a thin layer over Hamcrest matchers to allow for declarative assertions in your tests:


simplespec includes the following matchers by default, but you're encouraged to write your own:

  • x.must(equal(y)): Asserts x == y.
  • x.must(be(y)): A synonym for equal.
  • x.must(beA(klass)): Asserts that x is assignable as an instance of klass.
  • x.must(be(matcher)): Asserts that matcher applies to x.
  • x.must(not(be(matcher))): Asserts that matcher does not apply to x.
  • x.must(be(empty)): Asserts that x is a TraversableLike which is empty.
  • x.must(haveSize(n)): Asserts that x is a TraversableLike which has n elements.
  • x.must(contain(y)): Asserts that x is a SeqLike which contains the element y.
  • x.must(be(notNull)): Asserts that x is not null.
  • x.must(be(approximately(y, delta))): Asserts that x is within delta of y. Useful for floating-point math.
  • x.must(be(lessThan(2)): Asserts that x is less than 2.
  • x.must(be(greaterThan(2)): Asserts that x is greater than 2.
  • x.must(be(lessThanOrEqualTo(2)): Asserts that x is less than or equal to 2.
  • x.must(be(greaterThanOrEqualTo(2)): Asserts that x is greater than or equal to 2.
  • x.must(startWith("woo")): Asserts that string x starts with "woo".
  • x.must(endWith("woo")): Asserts that string x ends with "woo".
  • x.must(contain("woo")): Asserts that string x contains with "woo".
  • x.must(`match`(".*oo".r)): Asserts that string x matches the regular expression .*oo.

Matchers like be and not take matchers as their arguments, which means you can write domain-specific matchers for your tests:

class IsSufficientlyCromulentMatcher extends BaseMatcher[Fromulator] {
  def describeTo(description: Description) {
    description.appendText("a cromulemnt fromulator")

  def matches(item: AnyRef) = item match {
    case fromulator: Fromulator => fromulator.isCromulent
    case _ => false

trait CromulentMatcher {
  def cromulent = new IsSufficientlyCromulentMatcher

class BlahBlahSpec extends Spec with CromulentMatcher {
  class `A Fromulator` {
    val fromulator = new Fromulator

    def `is cromulent` = {

simplespec also includes two helper methods: evaluating and eventually.

evaluating captures a closure and allows you to make assertions about what happens when it's evaluated:

@Test def `throws an exception` = {
  evaluating {

eventually also captures a closure, but allows you to assert things about what happens when the closure is evaluated which might not be true the first few times:

@Test def `decay to zero` = {
  eventually {
  }.must(be(approximately(0.0, 0.001)))

See Matchers.scala for the full run-down.


Also, yeah, mocks. simplespec uses Mockito for its mocking stuff:

class PublisherSpec extends Spec {
  class `A publisher` {
    val message = mock[Message]

    val queue = mock[Queue]
    queue.enqueue(any).returns(0, 1, 2, 3)

    val publisher = new Publisher(queue)

    @Test def `sends a message to the queue` = {

See Mocks.scala for the full run-down.


Copyright (c) 2010-2012 Coda Hale

Copyright (c) 2012 Simple Finance Technology

Published under The MIT License, see LICENSE


A small Scala library for writing specs as simple classes and methods.







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