JUnit 4.5

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FAQ edited by Mike Clark. Web mastering by Erik Meade.
(see also JUnit.org)

8 August 2008

JUnit is a simple framework to write repeatable tests. It is an instance of the xUnit architecture for unit testing frameworks.

Summary of Changes in version 4.5


Basic JUnit operation


Extra Runners



Summary of Changes in version 4.4

JUnit is designed to efficiently capture developers' intentions about their code, and quickly check their code matches those intentions. Over the last year, we've been talking about what things developers would like to say about their code that have been difficult in the past, and how we can make them easier.


Two years ago, Joe Walnes built a new assertion mechanism on top of what was then JMock 1. The method name was assertThat, and the syntax looked like this:

assertThat(x, is(3));
assertThat(x, is(not(4)));
assertThat(responseString, either(containsString("color")).or(containsString("colour")));
assertThat(myList, hasItem("3"));

More generally:

assertThat([value], [matcher statement]);

Advantages of this assertion syntax include:

We have decided to include this API directly in JUnit. It's an extensible and readable syntax, and because it enables new features, like assumptions and theories.

Some notes:


Ideally, the developer writing a test has control of all of the forces that might cause a test to fail. If this isn't immediately possible, making dependencies explicit can often improve a design.
For example, if a test fails when run in a different locale than the developer intended, it can be fixed by explicitly passing a locale to the domain code.

However, sometimes this is not desirable or possible.
It's good to be able to run a test against the code as it is currently written, implicit assumptions and all, or to write a test that exposes a known bug. For these situations, JUnit now includes the ability to express "assumptions":

import static org.junit.Assume.*

@Test public void filenameIncludesUsername() {
   assumeThat(File.separatorChar, is('/'));
   assertThat(new User("optimus").configFileName(), is("configfiles/optimus.cfg"));

@Test public void correctBehaviorWhenFilenameIsNull() {
   assumeTrue(bugFixed("13356"));  // bugFixed is not included in JUnit
   assertThat(parse(null), is(new NullDocument()));

With this beta release, a failed assumption will lead to the test being marked as passing, regardless of what the code below the assumption may assert. In the future, this may change, and a failed assumption may lead to the test being ignored: however, third-party runners do not currently allow this option.

We have included assumeTrue for convenience, but thanks to the inclusion of Hamcrest, we do not need to create assumeEquals, assumeSame, and other analogues to the assert* methods. All of those functionalities are subsumed in assumeThat, with the appropriate matcher.

A failing assumption in a @Before or @BeforeClass method will have the same effect as a failing assumption in each @Test method of the class.


More flexible and expressive assertions, combined with the ability to state assumptions clearly, lead to a new kind of statement of intent, which we call a "Theory". A test captures the intended behavior in one particular scenario. A theory allows a developer to be as precise as desired about the behavior of the code in possibly infinite numbers of possible scenarios. For example:

public class UserTest {
  @DataPoint public static String GOOD_USERNAME = "optimus";
  @DataPoint public static String USERNAME_WITH_SLASH = "optimus/prime";

  @Theory public void filenameIncludesUsername(String username) {
    assumeThat(username, not(containsString("/")));
    assertThat(new User(username).configFileName(), containsString(username));

This makes it clear that the user's filename should be included in the config file name, only if it doesn't contain a slash. Another test or theory might define what happens when a username does contain a slash.

UserTest will attempt to run filenameIncludesUsername on every compatible DataPoint defined in the class. If any of the assumptions fail, the data point is silently ignored. If all of the assumptions pass, but an assertion fails, the test fails.

The support for Theories has been absorbed from the Popper project, and more complete documentation can be found there.

Defining general statements in this way can jog the developer's memory about other potential data points and tests, also allows automated tools to search for new, unexpected data points that expose bugs.

Other changes

This release contains other bug fixes and new features. Among them:

Summary of Changes in version 4.3.1

Summary of Changes with version 4.3

Summary of Changes with version 4.2

Summary of Changes with version 4.1

Summary of Changes with version 4.0

The architecture of JUnit 4.0 is a substantial departure from that of earlier releases. Instead of tagging test classes by subclassing junit.framework.TestCase and tagging test methods by starting their name with "test", you now tag test methods with the @Test annotation.

Contents of the Release

README.html  this file
junit-4.5.jar a jar file with the JUnit framework, bundled with the hamcrest-core-1.1 dependency.
junit-dep-4.5.jar a jar file with the JUnit framework, unbundled from any external dependencies. Choosing to use this jar developers will need to also provide in the classpath a compatible version of external dependencies (ie hamcrest-core-1.1+)
junit-4.5-src.jar a jar file with the source code of the JUnit framework
org/junit the source code of the basic JUnit annotations and classes
    samples sample test cases
    tests test cases for JUnit itself
javadoc javadoc generated documentation
doc documentation and articles


Below are the installation steps for installing JUnit:
  1. unzip the junit4.5.zip file
  2. add junit-4.5.jar to the CLASSPATH. For example: set classpath=%classpath%;INSTALL_DIR\junit-4.5.jar;INSTALL_DIR
  3. test the installation by running java org.junit.runner.JUnitCore org.junit.tests.AllTests.

  4. Notice: that the tests are not contained in the junit-4.5.jar but in the installation directory directly. Therefore make sure that the installation directory is on the class path
Important: don't install junit-4.5.jar into the extension directory of your JDK installation. If you do so the test class on the files system will not be found.

Getting Started

To get started with unit testing and JUnit read the article: JUnit Cookbook.
This article describes basic test writing using JUnit 4.

You find additional samples in the org.junit.samples package:


JUnit Cookbook
    A cookbook for implementing tests with JUnit.
    API documentation generated with javadoc.
Frequently asked questions
    Some frequently asked questions about using JUnit.
    The terms of the common public license used for JUnit.
The following documents still describe JUnit 3.8.

Test Infected - Programmers Love Writing Tests
    An article demonstrating the development process with JUnit.
JUnit - A cooks tour

Known Defects

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