_drupal_shutdown_function example

  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() {