class ShutdownFunctionTest

class ShutdownFunctionTest extends KernelTestBase {
  
  /**
   * Flag to indicate if ::shutdownOne() called.
   *
   * @var bool
   */
  protected $shutDownOneCalled = FALSE;
  
  /**
   * Flag to indicate if ::shutdownTwo() called.
   *
   * @var bool
   */
  protected $shutDownTwoCalled = FALSE;
  
  /**
   * Tests that shutdown functions can be added by other shutdown functions.
   */
  public function testShutdownFunctionInShutdownFunction() {
    // Ensure there are no shutdown functions registered before starting the
    // test.
    $this->assertEmpty(drupal_register_shutdown_function());
    // Register a shutdown function that, when called, will register another
    // shutdown function.
    drupal_register_shutdown_function([
      $this,
      'shutdownOne',
    ]);
    $this->assertCount(1, drupal_register_shutdown_function());
    // Simulate the Drupal shutdown.
    _drupal_shutdown_function();
    // Test that the expected functions are called.
    $this->assertTrue($this->shutDownOneCalled);
    $this->assertTrue($this->shutDownTwoCalled);
    $this->assertCount(2, drupal_register_shutdown_function());
  }
  
  /**
   * Tests shutdown functions by registering another shutdown function.
   */
  public function shutdownOne() {
    drupal_register_shutdown_function([
      $this,
      'shutdownTwo',
    ]);
    $this->shutDownOneCalled = TRUE;
  }
  
  /**
   * Tests shutdown functions by being registered during shutdown.
   */
  public function shutdownTwo() {
    $this->shutDownTwoCalled = TRUE;
  }

}