JUnit

"Junit" redirects here. For the Egyptian goddess, see Iunit.

JUnit

Developer(s)	Kent Beck, Erich Gamma, David Saff, Kris Vasudevan
Stable release	5.9.3 / April 26, 2023 (2023-04-26)
Repository	github.com/junit-team/junit5
Written in	Java
Operating system	Cross-platform
Type	Unit testing tool
License	Eclipse Public License 2.0 (relicensed previously)
Website	junit.org

JUnit is a unit testing framework for the Java programming language. JUnit has been important in the development of test-driven development, and is one of a family of unit testing frameworks which is collectively known as xUnit that originated with SUnit.

JUnit is linked as a JAR at compile-time. The latest version of the framework, JUnit 5, resides under package org.junit.jupiter. Previous versions JUnit 4 and JUnit 3 were under packages org.junit and junit.framework, respectively.

A research survey performed in 2013 across 10,000 Java projects hosted on GitHub found that JUnit (in a tie with slf4j-api) was the most commonly included external library. Each library was used by 30.7% of projects.

JUnit Life Cycle

Every JUnit test class usually has several test cases. These test cases are subject to the test life cycle. The full JUnit Life Cycle has three major phases:

1. Setup phase - This phase is where the test infrastrcture is prepared. Two levels of setup are available. The first type of setup is class-level setup in which a computationally expensive object, such as a database connection, is created and reused, with minimal side effects. Class-level setup is implemented using the @BeforeAll annotation. The other type is setup before running each test case, which uses the @BeforeEach annotation.
2. Text execution - This phase is responsible for running the test and verifying the result. The test result will indicate whether if the test result is a success or a failure. The @Test annotation is used here.
3. Clean up phase - After all posttest executions are performed, the systm may need to perform cleanup. Simiar to class-level setup, there is a corresponding class-level clean up. The @AfterAll annotation is used to support class-level clean up. The @AfterEach annotation allows for cleanup after test execution.

Integration with other tools

JUnit 5 integrates a number of tools, such as build tools, integrated development environments (IDE), continouous integration (CI) tools and many more.

Build Tools

JUnit supports Apache Ant, Apache Maven and Gradle build tools, which are the most widely used project build tools. Build tools are vital for automating the process of building the project.

Apache Ant, also known as Ant, is one of the build tools with the highest degree of versatility, and has the longest history out of the three build tools listed above. Ant centers around the "build.xml" file, used for configuring the tasks necessary to run a project.

In contrast to Ant, Apache Maven, also known as Maven, uses a standardized and unified approach to the build process. Maven follows the paradigm of "convention over configuration" for managing its dependencies. The Java source code (or "src") can be found under the "src/main/java" directory, and the test files can be found under the "src/test/java" directory. Maven can be used for any Java Project. It uses the Project Object Model (POM), which is an XML-based approach to configuring the build steps for the project. The minimal Maven with the "pom.xml" build file must contain a list of dependencies and a unique project identifier. Maven must be available on the build path to work.

Gradle is a build tool that borrows many concepts from its predecessors, Ant and Maven. It uses the build.gradle file to declare the steps required for the project build. Unlike Ant and Gradle, which are XML-based, Gradle requires the use of Apache Groovy, which is a Java-based programming language. Unlike Ant and Maven, Gradle does not require the use of XML. Gradle still adheres to Maven's "convention over configuration" approach, and follows the same structure for "src/main/java" and "src/test/java" directories.

Example of a JUnit test fixture

A JUnit test fixture is a Java object. Test methods must be annotated by the @Test annotation. If the situation requires it, it is also possible to define a method to execute before (or after) each (or all) of the test methods with the @BeforeEach (or @AfterEach) and @BeforeAll (or @AfterAll) annotations.

import org.junit.jupiter.api.*;

class FoobarTests {
    @BeforeAll
    static void setUpClass() throws Exception {
        // Code executed before the first test method
    }

    @BeforeEach
    void setUp() throws Exception {
        // Code executed before each test
    }
 
    @Test
    void oneThing() {
        // Code that tests one thing
    }

    @Test
    void anotherThing() {
        // Code that tests another thing
    }

    @Test
    void somethingElse() {
        // Code that tests something else
    }

    @AfterEach
    void tearDown() throws Exception {
        // Code executed after each test 
    }
 
    @AfterAll
    static void tearDownClass() throws Exception {
        // Code executed after the last test method 
    }
}

Previous versions of JUnit

According to Martin Fowler, one of the early adopters of JUnit:

JUnit was born on a flight from Zurich to the 1997 OOPSLA in Atlanta. Kent was flying with Erich Gamma, and what else were two geeks to do on a long flight but program? The first version of JUnit was built there, pair programmed, and done test first (a pleasing form of meta-circular geekery).

As a side effect of its wide use, previous versions of JUnit remain popular, with JUnit 4 having over 100,000 usages by other software components on the Maven Central repository.

In JUnit 4, the annotations for test execution callbacks were @BeforeClass, @Before, @After, and @AfterClass, as opposed to JUnit 5's @BeforeAll, @BeforeEach, @AfterEach, and @AfterAll.

In JUnit 3, test fixtures had to inherit from junit.framework.TestCase. Additionally, test methods had to be prefixed with 'test'.

See also

• xUnit, the family name given to testing frameworks including JUnit
• SUnit, the original Smalltalk version written by Kent Beck based on which JUnit was written
• TestNG, another test framework for Java
• Mock object, a technique used during unit testing
• Mockito, a mocking library to assist in writing tests
• EvoSuite, a tool to automatically generate JUnit tests
• List of Java Frameworks

References

• Gulati, Shekhar; Sharma, Rahul (2017). Java Unit Testing with JUnit 5. Apress.

External links

• Official website
• Irriger, Axel. "JUnit - Open Source Java Unit Testing Tool". Methods and Tools.
• "JUnit". Memory Not Found. Tutorials. Archived from the original on Jan 28, 2015.