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 thejunit-4.13.2.jarfile to the class path.

Practical case

Create a simple Java class namedCounter:

public class Counter { int count = 0; public void increment() { count++; } public int getCount() { return count; } }

Next, write a unit Test classCounterTestto testCounterclass:

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()); } }

intestIncrementmethod:

• The @Testannotation marks this method as a test method.
• UseassertTrueorassertEqualsto 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.
• TimeoutSet a time limit for the test method.

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