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Module 3: Testing

Module Overview

In this module, you'll learn comprehensive testing strategies for Java applications. You'll understand how to write effective unit tests, implement integration testing, and use JUnit and Mockito to verify your code's behavior.

Learning Objectives

Utilize an IDE's interactive debugger to identify why a unit test is failing
Implement a unit test that initializes state, executes a unit of code, and asserts that the state is as expected afterwards
Describe the purpose of a unit test
Outline the pattern GIVEN, WHEN, THEN for implementing a unit test
Remember that tests for empty arrays, out of bounds access, off by one errors, and null values should be included in unit test suites even if they're not in the use cases
Identify potential missing unit tests given a set of unit tests and use cases
Outline why a unit test should only test a single condition
Write a unit test that could only fail for a single reason
Recall that a deterministic test always produces the same outcome for the same inputs
Outline why unit tests should be deterministic

Key Topics

Unit Testing with JUnit

Learn how to write effective unit tests using the JUnit framework.

The Purpose of Unit Testing

Unit testing is a software development process where individual units of source code are tested to determine if they work correctly. Benefits include:

Finding bugs early in the development cycle
Ensuring code behaves as expected when making changes
Enabling safer refactoring by immediately revealing broken functionality
Providing documentation of expected behavior

The GIVEN-WHEN-THEN Pattern

The GIVEN-WHEN-THEN pattern is a structured approach to writing unit tests:

GIVEN: Set up the initial state or preconditions
WHEN: Perform the action being tested
THEN: Assert the expected outcomes

Example JUnit Test

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

public class CalculatorTest {
    
    @Test
    public void add_twoPositiveNumbers_returnsCorrectSum() {
        // GIVEN
        Calculator calculator = new Calculator();
        int a = 5;
        int b = 7;
        
        // WHEN
        int result = calculator.add(a, b);
        
        // THEN
        assertEquals(12, result, "5 + 7 should equal 12");
    }
    
    @Test
    public void divide_byZero_throwsArithmeticException() {
        // GIVEN
        Calculator calculator = new Calculator();
        int a = 10;
        int b = 0;
        
        // WHEN & THEN
        assertThrows(ArithmeticException.class, 
            () -> calculator.divide(a, b),
            "Division by zero should throw ArithmeticException");
    }
}

Testing Best Practices

Learn best practices for writing effective tests.

Test-Driven Development

Learn how to practice TDD by writing tests before implementation.

Integration Testing

Understand how to test the interactions between different components of your application.