White Box Testing Techniques

Learn white box testing techniques that examine internal code structure and logic

50 min•By Priygop Team•Last updated: Feb 2026

White Box Testing Principles

Tests internal code structure and logic
Requires knowledge of source code
Focuses on code coverage
Tests all code paths and branches
Validates internal logic and algorithms

Code Coverage Types

Example

// Statement Coverage
// Every line of code is executed at least once
function calculateGrade(score) {
    if (score >= 90) {        // Line 1
        return 'A';           // Line 2
    } else if (score >= 80) { // Line 3
        return 'B';           // Line 4
    } else if (score >= 70) { // Line 5
        return 'C';           // Line 6
    } else {                  // Line 7
        return 'F';           // Line 8
    }
}

// Test cases for 100% statement coverage
test('score 95 should return A', () => {
    expect(calculateGrade(95)).toBe('A'); // Covers lines 1, 2
});

test('score 85 should return B', () => {
    expect(calculateGrade(85)).toBe('B'); // Covers lines 1, 3, 4
});

test('score 75 should return C', () => {
    expect(calculateGrade(75)).toBe('C'); // Covers lines 1, 3, 5, 6
});

test('score 65 should return F', () => {
    expect(calculateGrade(65)).toBe('F'); // Covers lines 1, 3, 5, 7, 8
});

// Branch Coverage
// Every decision point is tested for both true and false
function validateUser(user) {
    if (user.age >= 18) {           // Branch 1: true/false
        if (user.email) {           // Branch 2: true/false
            return true;
        }
    }
    return false;
}

// Test all branch combinations
test('valid adult with email', () => {
    const user = { age: 25, email: 'test@example.com' };
    expect(validateUser(user)).toBe(true); // Branch 1: true, Branch 2: true
});

test('valid adult without email', () => {
    const user = { age: 25, email: null };
    expect(validateUser(user)).toBe(false); // Branch 1: true, Branch 2: false
});

test('minor with email', () => {
    const user = { age: 17, email: 'test@example.com' };
    expect(validateUser(user)).toBe(false); // Branch 1: false
});