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Learn How to Download JUnit 5 and Write Better Tests for Your Java Applications



How to Download JUnit 5




JUnit is one of the most popular unit testing frameworks for Java. It allows you to write and run tests that verify the functionality and quality of your code. JUnit 5 is the latest version of JUnit, which introduces many new features and improvements over JUnit 4.


In this article, we will show you how to download and use JUnit 5 in your Java projects. We will also cover some of the main features of JUnit 5 that make it a powerful and flexible testing tool.




download junit 5



What is JUnit 5 and Why Use It?




JUnit 5 is the next generation of JUnit. It consists of three main components:


  • JUnit Platform: a foundation for launching testing frameworks on the JVM.



  • JUnit Jupiter: a programming and extension model for writing tests and extensions in JUnit 5.



  • JUnit Vintage: a test engine for running JUnit 3 and JUnit 4 tests on the platform.



JUnit 5 leverages the features of Java 8 and above, such as lambda expressions, streams, and optional types. It also supports many different styles of testing, such as parameterized tests, dynamic tests, nested tests, and repeated tests. Moreover, it allows you to extend its functionality with custom annotations, conditions, and extensions.


Some of the benefits of using JUnit 5 are:


  • It is more modular and flexible than JUnit 4.



  • It is more expressive and readable than JUnit 4.



  • It is compatible with other testing frameworks and libraries.



  • It is supported by most IDEs and build tools.



Prerequisites




To use JUnit 5, you need to have:


  • Java 8 or higher installed on your machine.



  • Maven or Gradle as your build tool.



Downloading JUnit 5




You can download JUnit 5 using Maven or Gradle. In both cases, you need to add some dependencies to your project's configuration file.


Using Maven




If you are using Maven, you need to add the following dependency to your pom.xml file:


<dependency> <groupId>org.junit.jupiter</groupId> <artifactId>junit-jupiter-engine</artifactId> <version>5.9.2</version> <scope>test</scope> </dependency>


This dependency includes the junit-jupiter-api module, which contains the core annotations and assertions for writing tests, and the junit-jupiter-engine module, which contains the test engine implementation for running tests.


To run your tests using Maven, you can use the maven-surefire-plugin or the maven-failsafe-plugin. For example, you can run your tests with the following command:


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mvn test


Using Gradle




If you are using Gradle, you need to add the following dependency to your build.gradle file:


dependencies testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.9.2'


This dependency includes the junit-jupiter-api module and the junit-jupiter-engine module as well.


To run your tests using Gradle, you can use the test task provided by the java plugin. For example, you can run your tests with the following command:


gradle test


Conclusion




JUnit 5 Features and Examples




Now that we have downloaded JUnit 5, let's see some of the features that make it a powerful and flexible testing tool. We will also show some examples of how to use them in our tests.


Display Names




One of the new features of JUnit 5 is the ability to customize the display name of a test class or a test method. This can be useful for making the test names more descriptive and readable.


To set a custom display name, we can use the @DisplayName annotation. For example:


@DisplayName("A special test case") class DisplayNameDemo @Test @DisplayName("Custom test name containing spaces") void testWithDisplayNameContainingSpaces() @Test @DisplayName("") void testWithDisplayNameContainingSpecialCharacters() @Test @DisplayName("?") void testWithDisplayNameContainingEmoji()


The display names will be shown in the test reports and in the IDEs. For example, in IntelliJ IDEA, we can see something like this:



Assertions




Assertions are the core of any testing framework. They allow us to verify the expected behavior and outcome of our code. JUnit 5 provides a rich set of assertions in the org.junit.jupiter.api.Assertions class. Some of them are:


  • assertEquals(expected, actual): asserts that two objects are equal.



  • assertNotEquals(expected, actual): asserts that two objects are not equal.



  • assertTrue(condition): asserts that a condition is true.



  • assertFalse(condition): asserts that a condition is false.



  • assertNull(object): asserts that an object is null.



  • assertNotNull(object): asserts that an object is not null.



  • assertSame(expected, actual): asserts that two objects refer to the same instance.



  • assertNotSame(expected, actual): asserts that two objects do not refer to the same instance.



  • assertArrayEquals(expected, actual): asserts that two arrays are equal.



  • assertIterableEquals(expected, actual): asserts that two iterables are equal.



  • assertThrows(exceptionType, executable): asserts that an executable throws an exception of the specified type.



  • assertTimeout(duration, executable): asserts that an executable completes before a given timeout.



All these assertions accept an optional message parameter that can be used to provide additional information in case of a failure. For example:


@Test void testAssertEquals() assertEquals(2, 1 + 1, "1 + 1 should equal 2");


The message parameter can also be a supplier function that lazily evaluates the message only when needed. For example:


@Test void testAssertEqualsWithMessageSupplier() assertEquals(2, 1 + 1, () -> "1 + 1 should equal " + (1 + 1));


In addition to these assertions, JUnit 5 also supports lambda expressions for writing more concise and readable tests. For example, we can use assertAll to group multiple assertions into a single assertion. This allows us to execute all the assertions in a group even if one of them fails. For example:


@Test void testAssertAll() assertAll( () -> assertEquals(2, 1 + 1), () -> assertTrue('a' assertNotNull(new Object()) );


We can also use assertDoesNotThrow to verify that an executable does not throw any exception. For example:


@Test void testAssertDoesNotThrow() assertDoesNotThrow(() -> int x = 0; int y = 1 / x; );


Nested Tests




Nested tests are a feature of JUnit 5 that allow us to group related tests into nested classes. This can help us to structure our tests in a more hierarchical and organized way. Nested tests also inherit any annotations from their enclosing class, such as @BeforeEach or @AfterEach.


To create nested tests, we need to use the @Nested annotation on the nested class. For example:


@DisplayName("A stack") class StackTest { Stack Repeated Tests




Another feature of JUnit 5 is the ability to repeat a test multiple times with the @RepeatedTest annotation. This can be useful for testing scenarios that involve randomness, concurrency, or performance.


To create a repeated test, we need to use the @RepeatedTest annotation instead of the @Test annotation and specify the number of repetitions. For example:


@RepeatedTest(5) void repeatedTest() System.out.println("Repeating test"); assertTrue(Math.random() > 0.1);


This test will be executed five times and each time it will assert that a random number is greater than 0.1.


We can also customize the display name of each repetition using the name attribute of the @RepeatedTest annotation. We can use placeholders such as currentRepetition, totalRepetitions, and displayName to include dynamic information. For example:


@RepeatedTest(value = 5, name = "Repetition currentRepetition of totalRepetitions") void repeatedTestWithCustomDisplayName() System.out.println("Repeating test with custom display name"); assertTrue(Math.random() > 0.1);


The display names will be shown in the test reports and in the IDEs. For example, in IntelliJ IDEA, we can see something like this:



We can also access information about the current repetition and the total repetitions using the RepetitionInfo parameter. This parameter can be injected into the test method or into a @BeforeEach or @AfterEach method. For example:


@BeforeEach void beforeEach(RepetitionInfo repetitionInfo) int currentRepetition = repetitionInfo.getCurrentRepetition(); int totalRepetitions = repetitionInfo.getTotalRepetitions(); System.out.println("Before repetition " + currentRepetition + " of " + totalRepetitions); @RepeatedTest(5) void repeatedTestWithRepetitionInfo(RepetitionInfo repetitionInfo) System.out.println("Repeating test with repetition info"); assertTrue(Math.random() > 0.1); @AfterEach void afterEach(RepetitionInfo repetitionInfo) int currentRepetition = repetitionInfo.getCurrentRepetition(); int totalRepetitions = repetitionInfo.getTotalRepetitions(); System.out.println("After repetition " + currentRepetition + " of " + totalRepetitions); Dynamic Tests




Dynamic tests are a feature of JUnit 5 that allow us to generate tests at runtime. Unlike static tests, which are fully specified at compile time, dynamic tests can be created based on data, configuration, or other sources. This can be useful for testing scenarios that are not easy to express with static tests, such as loading test cases from an external resource, generating test cases based on some logic, or creating parameterized tests with complex arguments.


To create dynamic tests, we need to use the @TestFactory annotation on a method that returns a collection of DynamicTest instances. A DynamicTest consists of a display name and an executable code block. For example:


@TestFactory Collection dynamicTestsFromCollection() return Arrays.asList( DynamicTest.dynamicTest("First dynamic test", () -> assertTrue(true)), DynamicTest.dynamicTest("Second dynamic test", () -> assertEquals(4, 2 * 2)) );


This example creates two dynamic tests with different names and assertions. The @TestFactory method can also return an Iterable, an Iterator, or a Stream of DynamicTest instances. For example:


@TestFactory Stream dynamicTestsFromStream() return Stream.of("A", "B", "C") .map(str -> DynamicTest.dynamicTest("test" + str, () -> assertTrue(str.startsWith("A"))));


This example creates three dynamic tests based on a stream of strings. Each test has a name that includes the string and an assertion that checks if the string starts with "A".


Dynamic tests are executed differently than static tests and do not support lifecycle callbacks or extensions. Therefore, the @BeforeEach and @AfterEach methods will not be executed for dynamic tests. However, we can use the @BeforeAll and @AfterAll methods to perform setup and teardown operations for the entire test factory.


We can also use the TestInfo parameter to access information about the current dynamic test, such as its display name, tags, or unique ID. For example:


@TestFactory Stream dynamicTestsFromStreamWithTestInfo(TestInfo testInfo) assertEquals("dynamicTestsFromStreamWithTestInfo", testInfo.getDisplayName()); return Stream.of("A", "B", "C") .map(str -> DynamicTest.dynamicTest("test" + str, () -> assertTrue(str.startsWith("A"))));


This example asserts that the display name of the test factory method is equal to its method name. Parameterized Tests




Parameterized tests are a feature of JUnit 5 that allow us to run the same test multiple times with different arguments. They can help us to avoid duplication and increase test coverage. They use the @ParameterizedTest annotation instead of the @Test annotation. They also require a source of arguments, which can be provided by various annotations such as @ValueSource, @EnumSource, @MethodSource, @CsvSource, and @ArgumentsSource.


To create a parameterized test, we need to use the @ParameterizedTest annotation and specify a source of arguments. For example:


@ParameterizedTest @ValueSource(strings = "racecar", "radar", "able was I ere I saw elba") void palindromes(String candidate) assertTrue(Strings.isPalindrome(candidate));


This test will be executed three times and each time it will assert that the candidate string is a palindrome.


We can also use other types of arguments, such as ints, longs, doubles, booleans, enums, methods, csv files, etc. For example:


@ParameterizedTest @EnumSource(TimeUnit.class) void testWithEnumSource(TimeUnit timeUnit) assertNotNull(timeUnit);


This test will be executed six times and each time it will assert that the timeUnit enum value is not null.


We can also customize the display name of each invocation using the name attribute of the @ParameterizedTest annotation. We can use placeholders such as index, arguments, and displayName to include dynamic information. For example:


@ParameterizedTest(name = "index ==> the rank of ''0'' is 1") @CsvSource("apple, A", "banana, B", "cherry, C", "date, D") void testWithCustomDisplayNames(String fruit, String rank) assertNotNull(fruit); assertNotNull(rank);


The display names will be shown in the test reports and in the IDEs. For example, in IntelliJ IDEA, we can see something like this:


Extensions




Extensions are a feature of JUnit 5 that allow us to extend the behavior of test classes or methods. They can be used for various purposes, such as providing common setup and teardown logic, injecting dependencies, handling exceptions, skipping tests, etc.


To create an extension, we need to implement one or more extension APIs that correspond to different extension points in the test execution lifecycle. For example, we can implement the BeforeAllCallback interface to execute some code before all tests in a test class.


To register an extension, we can use one of the following methods:


  • Use the @ExtendWith annotation on a test class or a test method.



  • Use the @RegisterExtension annotation on a field in a test class.



  • Use the ServiceLoader mechanism to automatically register extensions.



For example, let's create an extension that connects to a database before all tests and disconnects after all tests. We can use the BeforeAllCallback and AfterAllCallback interfaces to implement this logic:


public class DatabaseExtension implements BeforeAllCallback, AfterAllCallback private Connection connection; @Override public void beforeAll(ExtensionContext context) throws Exception connection = DriverManager.getConnection("jdbc:h2:mem:test", "sa", ""); System.out.println("Connected to database"); @Override public void afterAll(ExtensionContext context) throws Exception connection.close(); System.out.println("Disconnected from database");


Then, we can register this extension using the @ExtendWith annotation on our test class:


@ExtendWith(DatabaseExtension.class) class DatabaseTest @Test void someTest() // use connection


We can also register multiple extensions using the same annotation. For example:


@ExtendWith(DatabaseExtension.class, LoggingExtension.class) class DatabaseTest @Test void someTest() // use connection and logger


JUnit 5 also provides some built-in extensions that we can use in our tests. For example, the TempDirectory extension creates and cleans up temporary directories for each test. We can use the @TempDir annotation to inject a Path or a File instance into our test method or test class. For example:


@ExtendWith(TempDirectory.class) class TempDirectoryTest @TempDir Path tempDir; @Test void writeItemsToFile() throws IOException Path file = tempDir.resolve("test.txt"); new ListWriter().writeItemsToFile(file); assertEquals(2, Files.readAllLines(file).size());


We can also create our own custom annotations that are composed of other annotations. For example, we can create an annotation that combines the @ExtendWith and @Tag annotations:


@Target( ElementType.TYPE, ElementType.METHOD ) @Retention(RetentionPolicy.RUNTIME) @Tag("database") @ExtendWith(DatabaseExtension.class) public @interface DatabaseTest


Then, we can use this annotation on our test class or test method instead of using multiple annotations:


@DatabaseTest class DatabaseTest @Test void someTest() // use connection Conclusion




In this article, we have learned how to download and use JUnit 5 in our Java projects. We have also explored some of the features of JUnit 5 that make it a powerful and flexible testing tool, such as display names, assertions, nested tests, repeated tests, dynamic tests, parameterized tests, and extensions.


JUnit 5 is a major improvement over JUnit 4 and provides many benefits for writing and running tests. It leverages the features of Java 8 and above and supports different styles of testing. It is also compatible with other testing frameworks and libraries and is supported by most IDEs and build tools.


If you want to learn more about JUnit 5, you can check out the following resources:


The official website of JUnit 5: [


The user guide of JUnit 5: [


The reference documentation of JUnit 5: [


The GitHub repository of JUnit 5: [


FAQs




Here are some frequently asked questions about JUnit 5:


Q: How do I migrate from JUnit 4 to JUnit 5?




A: You can use the junit-vintage-engine dependency to run your existing JUnit 4 tests on the JUnit platform. You can also use the junit-jupiter-migrationsupport module to use some of the JUnit 4 annotations in your JUnit 5 tests. For more details, see [


Q: How do I run JUnit 5 tests from the command line?




A: You can use the Console Launcher to run your JUnit 5 tests from the command line. You can download the jar file from [ and execute it with the java -jar command. For more details, see [


Q: How do I run JUnit 5 tests in Eclipse?




A: You need to have Eclipse Oxygen (4.7) or later to run JUnit 5 tests in Eclipse. You can use the Run As > JUnit Test option to run your tests as usual. You can also use the JUnit view to see the test results. For more details, see [


Q: How do I run JUnit 5 tests in IntelliJ IDEA?




A: You need to have IntelliJ IDEA 2016.2 or later to run JUnit 5 tests in IntelliJ IDEA. You can use the Run > Run... option to run your tests as usual. You can also use the Run tool window to see the test results. For more details, see [


Q: How do I write custom extensions for JUnit 5?




A: You can write custom extensions for JUnit 5 by implementing one or more extension APIs and registering them with the @ExtendWith annotation or other methods. You can also use the ExtensionContext parameter to access information about the current test execution. For more details, see [ 44f88ac181


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