Testing vs Debugging

// ═══════════════════════════════════════════════════
// TESTING (Tester's Perspective) - What does it DO?
// ═══════════════════════════════════════════════════

// Tester runs this test and discovers a FAILURE:
test("login should succeed with valid credentials", () => {
    const result = login("alice@example.com", "SecurePass123");
    expect(result.success).toBe(true);  // ❌ FAILS - result.success is false
    expect(result.token).toBeDefined(); // ❌ FAILS - no token returned
});
// Tester's job is DONE: they file a bug report with:
// - Steps to reproduce
// - Expected result: success=true, token present
// - Actual result: success=false, no token
// - Severity: Critical (blocks login)

// ═══════════════════════════════════════════════════
// DEBUGGING (Developer's Perspective) - WHY did it fail?
// ═══════════════════════════════════════════════════

// Developer investigates and finds the bug:
function login(email, password) {
    const user = db.findUser(email);
    // BUG: Missing null check - if user not found, this crashes
    // and returns undefined instead of { success: false }
    if (user.password === hash(password)) {  // TypeError: Cannot read 'password' of undefined
        return { success: true, token: generateToken(user) };
    }
    return { success: false };
}

// Developer FIXES the bug:
function login(email, password) {
    const user = db.findUser(email);
    if (!user) {
        return { success: false, message: "User not found" };
    }
    if (user.password === hash(password)) {
        return { success: true, token: generateToken(user) };
    }
    return { success: false, message: "Invalid password" };
}
// After fix: developer notifies tester → tester retests → verifies fix