JUnit Unit Testing Framework: A Beginner's Tutorial

JUnit is a unit testing framework for Java that provides simple tools to test application components. Once the dependencies are installed, you can test a class by writing a unit test class that contains the @Test annotation and verify expected and actual values ​​using assertion methods such as assertEquals. JUnit provides many features such as prepare methods, failure messages, and timeout mechanisms.

JUnit Unit Testing Framework: Beginner’s Tutorial

Introduction

JUnit is A widely used unit testing framework in the Java language. It provides a concise yet powerful set of tools that enable developers to easily test application components.

Install

Dependency Manager. Add the following line of dependencies:

dependencies {
  testImplementation "junit:junit:4.13.2"
}

If downloading manually, add the junit-4.13.2.jar file to the class path.

Practical case

Create a simple Java class named Counter:

public class Counter {

    int count = 0;

    public void increment() {
        count++;
    }

    public int getCount() {
        return count;
    }
}

Next, write a unit Test class CounterTest to test Counter class:

import static org.junit.Assert.*;

public class CounterTest {

    @Test
    public void testIncrement() {
        Counter counter = new Counter();

        // 执行待测试方法
        counter.increment();

        // 断言预期值和实际值相等
        assertEquals(1, counter.getCount());
    }
}

in testIncrement method:

• The @Test annotation marks this method as a test method.
• Use assertTrue or assertEquals to assert that expected results match actual results.

Run the test

Run the test from the command line using the following command:

mvn test

Assertion

JUnit provides a variety of assertion methods, including:

• assertTrue: Tests that the actual value is true.
• assertFalse: Test that the actual value is false.
• assertEquals: Tests that expected and actual values ​​are equal.
• assertNotEquals: Tests that the expected value and the actual value are not equal.

Other features

• Preparation methods (BeforeEach/AfterEach) Executed before/after each test method.
• Failure Message (fail) Display a custom message when the test fails.
• Timeout Set a time limit for the test method.

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