Что такое PHPUnit?

PHPUnit - стандартный фреймворк для тестирования PHP. Создан Себастьяном Бергманном.

use PHPUnit\Framework\TestCase;

class UserServiceTest extends TestCase {
    protected function setUp(): void {
        $this->service = new UserService();
    }

    public function testCreateUser(): void {
        $user = $this->service->create('John', 'john@mail.com');
        $this->assertInstanceOf(User::class, $user);
        $this->assertEquals('John', $user->name);
    }

    #[DataProvider('emailProvider')]
    public function testValidateEmail(string $email, bool $expected): void {
        $this->assertEquals($expected, $this->service->validateEmail($email));
    }

    public static function emailProvider(): array {
        return [
            ['test@mail.com', true],
            ['invalid', false],
        ];
    }
}