Introduction

JUnit is one of the most popular unit-testing frameworks in the Java ecosystem. The JUnit 5 version contains a number of exciting innovations, with the goal to support new features in Java 8 and above, as well as enabling many different styles of testing.

Unlike previous versions of JUnit, JUnit 5 is composed of several different modules from three different sub-projects.

JUnit 5 = JUnit Platform + JUnit Jupiter + JUnit Vintage

The JUnit Platform serves as a foundation for launching testing frameworks on the JVM. It also defines the TestEngineAPI for developing a testing framework that runs on the platform. Furthermore, the platform provides a Console Launcher to launch the platform from the command line and a JUnit 4 based Runner for running any TestEngine on the platform in a JUnit 4 based environment. First-class support for the JUnit Platform also exists in popular IDEs (see IntelliJ IDEA, Eclipse) and build tools (see Gradle, Maven).

JUnit Jupiter is the combination of the new programming model and extension model for writing tests and extensions in JUnit 5. The Jupiter sub-project provides a TestEngine for running Jupiter based tests on the platform.

JUnit Vintage provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the platform.

What's new

Below you have just a taste of some of the new features JUnit 5 has got to offer. Check out the user guide for a more complete list.

@DisplayName 
A display name can now be set for a test. This will be shown instead of the method name and will make output both easier to read and format. You can even include spaces and emojis.

@DisplayName("Single test successful")
@Test
void successTest() {
    log.info("Success");
}

Dynamic Tests
Dynamic on-the-fly tests can be made using @TestFactory and lambdas. These tests must return instances of Streams, Collections, Iterables, or Iterators of DynamicNode instances. These cases are executed lazily and so is generated at run-time.

@TestFactory
Collection<DynamicTest> dynamicTestsFromCollection() {
   return Arrays.asList(
      dynamicTest("Test True", () -> assertTrue(true)),
      dynamicTest("Test Equals", () -> assertEquals(5, 2 + 3))
   );
}

Multiple assertions at once
We now have the power to group assertions together using the assertAll method. It will process all of the assertions in a group even if one fails. Then it will let us know which assertions failed at the end so we do not have to fix and rerun one at a time.

@Test
void multipleAssertionsTest() {
    assertAll( 
  		() -> assertEquals(1, 2), 
  		() -> assertTrue(3 < 4), 
	);
}

Assumptions
These were already present in JUnit 4 but I thought they were worth a mention because in JUnit 5 they can also use Java 8 lambdas. According to the JUnit 5 user guide “Assumptions provide a basic form of dynamic behavior but are intentionally rather limited in their expressiveness”. They are useful because a failed Assumption does not fail a test,  it aborts it. This is useful if you only want to perform tests under certain conditions like on certain platforms or only if certain variables are present in the current runtime environment.

@Test
void testOnlyOnCertainMachines() {
   assumeTrue("dev".equals(System.getenv("ENV")),
   () -> "Aborting test as not needed on this computer");
   // rest of the test to run
}

ParameterizedTests
These allow you to run a test case multiple times with different arguments. These arguments can be strings, literal values, methods, Enums, CSV files, etc. @ParameterisedTest ultimately lets you avoid using unnecessary testing loops or duplicating test code.

@ParameterizedTest
@ValueSource(ints = { 1, 2, 3 })
void testWithValueSource(int argument) {
   assertTrue(argument > 0 && argument < 4);
}

Declarative Timeouts
@Timeout isn’t limited to being placed on test cases themselves. Along with the aforementioned test cases, @Timeout can also be placed at the type level, where it will provide a default timeout for all test cases declared in the class, this can be overridden by adding a @Timeout to a test case. @Timeout can also be added to lifecycle methods, @BeforeAll, @BeforeEach​, @AfterEach, @AfterAll​.

@Test
@Timeout(unit = TimeUnit.MILLISECONDS, value = 500L) // Default unit is seconds, but other options available
public void testTestCaseTimeout() throws InterruptedException {
	Thread.sleep(600);
}

Asserting exceptions

The @Testannotation no longer takes an expected argument. The Jupiter API provides a much tidier way of writing this type of test.

@Test
void exceptionThrownIfTryToSetAlertStatusToNull() {
  IllegalArgumentException actual = assertThrows(IllegalArgumentException.class,
                                                 () -> testee.setAlertStatus(null));
  assertEquals("Alert status cannot be set to null.", actual.getMessage());
}

Migration from JUnit 4

Although the JUnit Jupiter programming model and extension model will not support JUnit 4 features such as Rules and Runners natively, it is not expected that source code maintainers will need to update all of their existing tests, test extensions, and custom build test infrastructure to migrate to JUnit Jupiter.

Maven dependencies

<dependencies>
		<dependency>
			<groupId>org.junit.jupiter</groupId>
			<artifactId>junit-jupiter-api</artifactId>
			<version>${junit.jupiter.version}</version>
			<scope>test</scope>
		</dependency>
		<dependency>
			<groupId>org.junit.jupiter</groupId>
			<artifactId>junit-jupiter-engine</artifactId>
			<version>${junit.jupiter.version}</version>
			<scope>test</scope>
		</dependency>
        <dependency> <!-- temporary until all junit4 tests have been migrated -->
			<groupId>junit</groupId>
			<artifactId>junit</artifactId>
			<version>${junit.version}</version>
			<scope>test</scope>
		</dependency>
		<dependency> <!-- temporary until all junit4 tests have been migrated -->
			<groupId>org.junit.vintage</groupId>
			<artifactId>junit-vintage-engine</artifactId>
			<version>${junit.vintage.version}</version>
			<scope>test</scope>
		</dependency>
	</dependencies>

Running JUnit 4 Tests on the JUnit Platform

Just make sure that the junit-vintage-engine artifact is in your test runtime path. In that case JUnit 4 tests will automatically be picked up by the JUnit Platform launcher.

Migration Tips

The following are topics that you should be aware of when migrating existing JUnit 4 tests to JUnit Jupiter.

• Annotations reside in the org.junit.jupiter.api package.

• Assertions reside in org.junit.jupiter.api.Assertions.

  • Note that you may continue to use assertion methods from org.junit.Assert or any other assertion library such as AssertJ, Hamcrest, Truth, etc.

• Assumptions reside in org.junit.jupiter.api.Assumptions.

  • Note that JUnit Jupiter 5.4 and later versions support methods from JUnit 4’s org.junit.Assume class for assumptions. Specifically, JUnit Jupiter supports JUnit 4’s AssumptionViolatedException to signal that a test should be aborted instead of marked as a failure.

• @Before and @After no longer exist; use @BeforeEach and @AfterEach instead.

• @BeforeClass and @AfterClass no longer exist; use @BeforeAll and @AfterAll instead.

• @Ignore no longer exists: use @Disabled or one of the other built-in execution conditions instead

  • See also JUnit 4 @Ignore Support.

• @Category no longer exists; use @Tag instead.

• @RunWith no longer exists; superseded by @ExtendWith.

• @Rule and @ClassRule no longer exist; superseded by @ExtendWith and @RegisterExtension

  • See also Limited JUnit 4 Rule Support.