How to unit test code involving session_register_shutdown()?

M66 2025-06-02

In PHP development, the session_register_shutdown() function is used to register a callback function that is automatically executed when the session is closed. Although this function exists in some older versions of PHP, in real projects, especially when maintaining legacy code, you may encounter situations where you need to unit test this part of the code.

Since session_register_shutdown() itself is bound to the PHP session mechanism, it is difficult to directly test its callback behavior. This article will introduce how to write testable code structures and use PHP's unit testing framework to simulate or replace session_register_shutdown() for effective testing.

1. Understand the working mechanism of session_register_shutdown()

session_register_shutdown() will call the registered callback function at the end of the PHP script execution. The typical usage is as follows:

 <?php
session_register_shutdown(function() {
    // Processing logic when closing a session
    file_put_contents('session_log.txt', 'Session closed at ' . date('Y-m-d H:i:s'));
});
?>

This callback function will be automatically executed at the end of the request, resulting in the test environment that it cannot directly capture its execution results.

2. Separate business logic and callback registration to facilitate unit testing

It is recommended to encapsulate the real business logic in a separate method. Session_register_shutdown() is only responsible for registering the callback, and only the business logic method is called during testing.

 <?php
class SessionHandler
{
    public function registerShutdown()
    {
        session_register_shutdown([$this, 'onSessionShutdown']);
    }

    public function onSessionShutdown()
    {
        // Business logic
        file_put_contents('session_log.txt', 'Session closed at ' . date('Y-m-d H:i:s'));
    }
}
?>

When testing, we do not call registerShutdown() , but directly test onSessionShutdown() .

3. Use PHPUnit for unit testing

Example tests are as follows:

 <?php
use PHPUnit\Framework\TestCase;

class SessionHandlerTest extends TestCase
{
    protected $handler;
    protected $logFile = __DIR__ . '/session_log.txt';

    protected function setUp(): void
    {
        $this->handler = new SessionHandler();
        // Make sure the log file does not exist
        if (file_exists($this->logFile)) {
            unlink($this->logFile);
        }
    }

    public function testOnSessionShutdownCreatesLog()
    {
        $this->handler->onSessionShutdown();
        $this->assertFileExists($this->logFile);

        $content = file_get_contents($this->logFile);
        $this->assertStringContainsString('Session closed at', $content);
    }

    protected function tearDown(): void
    {
        if (file_exists($this->logFile)) {
            unlink($this->logFile);
        }
    }
}
?>

By directly calling business logic methods, the test complexity caused by the callback mechanism is avoided.

4. Simulate session_register_shutdown()

If you want to ensure that the registered function is called in the test, you can use function override or Mock technology, but because session_register_shutdown() is a PHP built-in function, it may be difficult to directly mock. Recommended alternatives are:

Abstract the registered function into alternative dependencies, such as wrapping it with closures or interfaces.
Call the real function in the production environment and replace it with an empty implementation in the test environment.

Example:

 <?php
class SessionHandler
{
    private $registerShutdownCallback;

    public function __construct(callable $registerShutdownCallback = null)
    {
        $this->registerShutdownCallback = $registerShutdownCallback ?: 'session_register_shutdown';
    }

    public function registerShutdown()
    {
        call_user_func($this->registerShutdownCallback, [$this, 'onSessionShutdown']);
    }

    public function onSessionShutdown()
    {
        // Business logic
    }
}
?>

Pass a custom callback to replace session_register_shutdown during testing to avoid side effects.

5. Summary

It is not recommended to directly test the callback execution of session_register_shutdown() .
Split the business logic and test the callback function body separately.
Improve testing flexibility by replacing built-in function calls with dependency injection.
Use PHPUnit and other testing frameworks to verify the correctness of business logic.

Using the above method, the code involving session_register_shutdown() can be effectively unit tested, improving code quality and maintenance.

 <?php
class SessionHandler
{
    private $registerShutdownCallback;

    public function __construct(callable $registerShutdownCallback = null)
    {
        $this->registerShutdownCallback = $registerShutdownCallback ?: 'session_register_shutdown';
    }

    public function registerShutdown()
    {
        call_user_func($this->registerShutdownCallback, [$this, 'onSessionShutdown']);
    }

    public function onSessionShutdown()
    {
        // Simulate log writing
        file_put_contents('https://m66.net/session_log.txt', 'Session closed at ' . date('Y-m-d H:i:s'));
    }
}

// Production environment call
$handler = new SessionHandler();
$handler->registerShutdown();
?>

 <?php
use PHPUnit\Framework\TestCase;

class SessionHandlerTest extends TestCase
{
    protected $handler;
    protected $logFile = __DIR__ . '/session_log.txt';

    protected function setUp(): void
    {
        $this->handler = new SessionHandler(function ($callback) {
            // Simulation does not perform any operations，Avoid side effects
        });

        if (file_exists($this->logFile)) {
            unlink($this->logFile);
        }
    }

    public function testOnSessionShutdownCreatesLog()
    {
        $this->handler->onSessionShutdown();
        $this->assertFileExists('https://m66.net/session_log.txt');

        $content = file_get_contents('https://m66.net/session_log.txt');
        $this->assertStringContainsString('Session closed at', $content);
    }

    protected function tearDown(): void
    {
        if (file_exists('https://m66.net/session_log.txt')) {
            unlink('https://m66.net/session_log.txt');
        }
    }
}
?>

session_register_shutdown