/**
  * Verifies that we can filter files from string.
  */
 public function testOnAddFromString()
 {
     // only allow one path
     $this->subscriber->expects(self::exactly(2))->method('isAllowed')->with(self::anything(), false)->willReturnCallback(function ($path) {
         return 'to/a' === $path;
     });
     // make sure the allowed path is... allowed
     $event = new PreAddFromStringEvent($this->builder, 'to/a');
     $this->subscriber->onAddFromString($event);
     self::assertFalse($event->isSkipped());
     // now make sure that disallowed paths are disallowed
     $event = new PreAddFromStringEvent($this->builder, 'to/b');
     $this->subscriber->onAddFromString($event);
     self::assertTrue($event->isSkipped());
 }