public function testIsStackable()
{
$this->assertFalse($this->stack->isStackable('files://a.jpg'), 'Files on stack should not be stackable');
$this->assertFalse($this->stack->isStackable('files://non_existent_file.txt'), 'Non existent files should not be stackable');
$this->assertFalse($this->stack->isStackable('files://evil.exe'), 'Unaccepted file extensions should not be stackable');
}