[JAVA] How to use JUnit 5

This article is from MDC Advent Calendar 2020 Day 19.


Do you guys write unit tests? (I myself haven't written much recently ...)

--I can implement it, but I can't write much test code --I've written up to JUnit4, but JUnit5 doesn't have much ...

We hope this will help you get started writing test code in JUnit 5 for those who are surprisingly many.


What is JUnit 5

—— Needless to say, it's the most major testing framework in Java development. --Unlike previous versions of JUnit, JUnit 5 consists of multiple modules contained in three subprojects. JUnit 5 = JUnit Platform + JUnit Jupiter + JUnit Vintage

――It's been a long time, but if you want to start writing tests with JUnit 5 for the time being, you can add ** JUnit Jupiter ** to the dependency (the following is a sample of gradle)


plugins {
    id "java"

sourceCompatibility = 8
targetCompatibility = 8
[compileJava, compileTestJava]*.options*.encoding = "UTF-8"

repositories {

dependencies {
    testImplementation "org.junit.jupiter:junit-jupiter:5.7.0"

Supported Java versions

--Java 8 or above is required to run JUnit5

How to write a test

Test method

package sample.junit5;

import org.junit.jupiter.api.Test;

import static org.junit.jupiter.api.Assertions.assertEquals;

class JUnit5Test {

    void success() {
        assertEquals(12, 12);

    void failure() {
        assertEquals(5, 12);
Annotation Explanation
@Test The given method becomes a test method

--Use the assertion method (eg assertEquals (expected, actual)) to compare the expected and measured values --Actually, call the method under test and compare its return value with the expected value. --In JUnit5, both test classes and test methods no longer need to be public.

Pre-processing / post-processing

package sample.junit5;

import org.junit.jupiter.api.*;

class JUnit5Test {

    static void beforeAll() {
        System.out.println("☆ beforeAll()");

    void beforeEach() {
        System.out.println("☆☆ beforeEach()");

    void afterEach() {
        System.out.println("★★ afterEach()");

    static void afterAll() {
        System.out.println("★ afterAll()");

    void test1() {
        System.out.println("~~~ test1() ~~~");

    void test2() {
        System.out.println("~~~ test2() ~~~");

Execution result

☆ beforeAll()
☆☆ beforeEach()
~~~ test1() ~~~
★★ afterEach()
☆☆ beforeEach()
~~~ test2() ~~~
★★ afterEach()
★ afterAll()
Annotation Explanation
@BeforeAll The given method is executed only once at the very beginning
Method must be static
@BeforeEach The given method is executed every time before each test method
@AfterAll The given method is executed only once at the very end
Method must be static
@AfterEach The given method is executed after each test method

Test grouping

package sample.junit5;

import org.junit.jupiter.api.*;

class JUnit5Test {

    void test1() {...}

    class group1 {
        void test2() {...}

        void test3() {...}
Annotation Explanation
@Nested Test classes can be nested by giving them to non-static classes

――The test class often has a certain number of steps, so it is recommended to group by test viewpoint.

Parameter test

package sample.junit5;

import org.junit.jupiter.params.ParameterizedTest;
import org.junit.jupiter.params.provider.ValueSource;

class JUnit5Test {

    @ValueSource(strings = {"foo", "bar", "baz"})
    void test(String value) {
        System.out.println("VALUE: " + value);

Execution result

VALUE: foo
VALUE: bar
VALUE: baz
Annotation Explanation
@ParameterizedTest The given method becomes a parameter test
@ValueSource You can specify one array of literal values ​​and provide one parameter in the parameter test call (eg String)

--It is an image that the test is executed for the number of parameters --The following literal values ​​are provided


――I'm sorry, I haven't had enough time to write half of what I want to write (... I started writing after 23:00 on 12/18). --Anyway, JUnit 5 is convenient and easy --Everyone, let's write the test code properly


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