How can PHPUnit be utilized to test different aspects of an online shop application, such as user authentication, order processing, and database interactions?

PHPUnit can be utilized to test different aspects of an online shop application by writing test cases for user authentication, order processing, and database interactions. These test cases can simulate different scenarios and ensure that the application functions as expected. By using PHPUnit assertions, developers can verify the correctness of the code and catch any potential bugs early in the development process.

// Example PHPUnit test case for user authentication
use PHPUnit\Framework\TestCase;

class UserAuthenticationTest extends TestCase {
    public function testUserLogin() {
        // Simulate user login process
        $user = new User();
        $isLoggedIn = $user->login('username', 'password');
        
        $this->assertTrue($isLoggedIn);
    }
}