TDD — Test Driven Development

Test-Driven Development

TDD cycle: Red → Green → Refactor

// 1. RED — Write a failing test first
public function testPasswordMustHaveUppercase(): void {
    $validator = new PasswordValidator();
    $this->assertFalse($validator->validate("alllowercase1!"));
}

// 2. GREEN — Write minimum code to pass
class PasswordValidator {
    public function validate(string $password): bool {
        return preg_match("/[A-Z]/", $password) === 1;
    }
}

// 3. REFACTOR — improve without breaking tests
class PasswordValidator {
    private array $rules = [
        "uppercase" => "/[A-Z]/",
        "digit"     => "/[0-9]/",
        "special"   => "/[!@#$%]/",
        "length"    => "/.{8,}/",
    ];

    public function validate(string $password): bool {
        foreach ($this->rules as $rule => $pattern) {
            if (!preg_match($pattern, $password)) return false;
        }
        return true;
    }
}

// 4. Repeat for next feature