Java Unit Testing Examples

This repository serves as a reference implementation of unit testing best practices in Java applications.

Overview

This project demonstrates how to implement robust unit tests for Java applications using industry-standard frameworks and methodologies.

🧪 Testing Approach

The examples in this repository showcase:

• JUnit 5 Implementation - Utilizing the latest features of JUnit Jupiter for comprehensive test coverage
• Test-Driven Development (TDD) - Demonstrating how to write tests before implementation
• Clean Test Architecture - Following the Arrange-Act-Assert pattern for readable and maintainable tests

🛠️ Example Test Structure

🧮 Calculator Example

public class CalculatorTest {

    @Test
    @DisplayName("Simple addition")
    public void testAdd() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result);
    }

    @Test
    @DisplayName("Division by zero")
    public void testDivideByZero() {
        Calculator calculator = new Calculator();
        assertThrows(ArithmeticException.class, () -> calculator.divide(10, 0));
    }
}

🧑‍💻 Java Developer Example

public class JavaDeveloperTest {
    @Test
    @DisplayName("Should demonstrate core skills")
    public void testDemonstrateSkills() {
        // Arrange
        JavaDeveloper developer = new JavaDeveloper();

        // Act
        List<String> skills = developer.getTestingSkills();

        // Assert
        assertAll(
                () -> assertTrue(skills.contains("JUnit")),
                () -> assertTrue(skills.contains("TestNG")),
                () -> assertTrue(skills.contains("Mockito")),
                () -> assertTrue(skills.contains("Spring")),
                () -> assertTrue(skills.contains("TDD"))
        );
    }

    @Test
    @DisplayName("Should know JUnit")
    public void testKnowsJUnit() {
        assertTrue(new JavaDeveloper().getTestingSkills().contains("JUnit"));
    }

    @Test
    @DisplayName("Should know TestNG")
    public void testKnowsTestNG() {
        assertTrue(new JavaDeveloper().getTestingSkills().contains("TestNG"));
    }
}

🔍 Frameworks & Tools Demonstrated

• JUnit 5 - The foundation of the testing strategy in this repository
• • Maven/Gradle - For build automation and test execution

📋 Additional Frameworks For Further Exploration

• TestNG - For more complex testing scenarios requiring advanced features
• Mockito - For mocking external dependencies and isolating units under test
• Continuous Integration - Automated testing pipelines with Jenkins/GitHub Actions

📊 Best Practices Demonstrated

1. Independent Tests - Each test runs in isolation without dependencies on other tests
2. Edge Case Coverage - Testing boundary conditions and error scenarios
3. Descriptive Test Names - Using @DisplayName for human-readable test documentation
4. High Code Coverage - Aiming for comprehensive coverage of all code paths
5. Mock External Dependencies - Isolating units from external resources for true unit testing

🏗️ Project Structure

src/
├── main/java/
│   └── code/
│       ├── JavaDeveloper.java
│       └── Calculator.java
└── test/java/
    └── code/
        ├── JavaDeveloperTest.java
        └── CalculatorTest.java

📚 Further Learning Topics

Advanced testing concepts demonstrated in different branches:

• Parameterized tests using JUnit 5
• Test lifecycle hooks
• Exception testing techniques
• Custom test extensions
• Test suites organization

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"Code without tests is bad code. It doesn't matter how well written it is; it doesn't matter how pretty or object-oriented or well-encapsulated it is. With tests, we can change the behavior of our code quickly and verifiably. Without them, we really don't know if our code is getting better or worse." — Michael Feathers