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Introduction to JUnit 5

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JUnit 5 is the latest version of the popular Java testing framework, JUnit. It introduces several new features and improvements over its predecessors, making it more flexible and powerful for modern testing needs. This module will provide an overview of JUnit 5, its architecture, and the key differences from JUnit 4.

Key Concepts

  1. JUnit 5 Architecture

JUnit 5 is composed of three main modules:

  • JUnit Platform: This is the foundation for launching testing frameworks on the JVM. It defines the TestEngine API for developing new testing frameworks.
  • JUnit Jupiter: This module includes new programming and extension models for writing tests and extensions in JUnit 5.
  • JUnit Vintage: This module provides a TestEngine for running JUnit 3 and JUnit 4 based tests on the JUnit 5 platform.

  1. New Features in JUnit 5

JUnit 5 introduces several new features and improvements:

  • New Annotations: JUnit 5 provides new annotations such as @TestFactory, @Nested, @DisplayName, and more.
  • Dynamic Tests: Allows the creation of tests at runtime.
  • Improved Extension Model: More powerful and flexible extension model compared to JUnit 4.
  • Parameter Injection: Supports dependency injection for constructors and methods.

  1. Compatibility

JUnit 5 is designed to be backward compatible with JUnit 4 and JUnit 3 through the JUnit Vintage module. This allows you to run older tests alongside new ones without major changes.

Practical Example

Let's start with a simple example to demonstrate the basic structure of a JUnit 5 test.

Example: Basic JUnit 5 Test

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

public class CalculatorTest {

    @Test
    void addition() {
        Calculator calculator = new Calculator();
        assertEquals(2, calculator.add(1, 1), "1 + 1 should equal 2");
    }
}

class Calculator {
    int add(int a, int b) {
        return a + b;
    }
}

Explanation

  • @Test: This annotation is used to mark a method as a test method.
  • assertEquals: This assertion checks if the expected value (2) is equal to the actual value returned by the add method.

Practical Exercise

Exercise: Write a JUnit 5 Test for Subtraction

  1. Create a Calculator class with a subtract method.
  2. Write a JUnit 5 test class CalculatorTest.
  3. Add a test method subtraction to test the subtract method.

Solution

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

public class CalculatorTest {

    @Test
    void subtraction() {
        Calculator calculator = new Calculator();
        assertEquals(0, calculator.subtract(1, 1), "1 - 1 should equal 0");
    }
}

class Calculator {
    int subtract(int a, int b) {
        return a - b;
    }
}

Common Mistakes

  • Forgetting to import JUnit 5 annotations: Ensure you import org.junit.jupiter.api.Test and other necessary classes.
  • Incorrect assertion methods: Use the appropriate assertion methods provided by JUnit 5.

Summary

In this section, we introduced JUnit 5, its architecture, and key features. We also provided a practical example and exercise to help you get started with writing JUnit 5 tests. Understanding these basics will prepare you for more advanced topics in JUnit 5.

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