How to use JUnit 5

This article is from MDC Advent Calendar 2020 Day 19.

Introduction

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.

Overview

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

• JUnit Platform --The basis for launching the test framework on the JVM --Defines the TestEngine API for developing test frameworks that run on the above platforms --Provides Console Launcher to launch the platform from the command line, build plugins for Gradle and Maven, JUnit4-based test runners, etc. so that you can run any TestEngine.
• JUnit Jupiter --A summary of the minimum dependencies required to write tests in JUnit5
• JUnit Vintage --Provide a TestEngine to run JUnit3 or JUnit4-based tests

――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)

build.gradle

plugins {
    id "java"
}

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

repositories {
    mavenCentral()
}

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 {

    @Test
    void success() {
        assertEquals(12, 12);
    }

    @Test
    void failure() {
        assertEquals(5, 12);
    }
}

--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 {

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

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

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

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

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

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

Execution result

☆ beforeAll()
☆☆ beforeEach()
~~~ test1() ~~~
★★ afterEach()
☆☆ beforeEach()
~~~ test2() ~~~
★★ afterEach()
★ afterAll()

Test grouping

package sample.junit5;

import org.junit.jupiter.api.*;

class JUnit5Test {

    @Test
    void test1() {...}

    @Nested
    class group1 {
        @Test
        void test2() {...}

        @Test
        void test3() {...}
    }
}

――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 {

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

Execution result

VALUE: foo
VALUE: bar
VALUE: baz

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

• short
• byte
• int
• long
• float
• double
• char
• java.lang.String
• java.lang.Class

Finally

――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

reference

• JUnit 5 User Guide