Cachearium\CacheAbstract::appendCallback PHP Method

    public function appendCallback(callable $callback)
    {
        // @codeCoverageIgnoreStart
        if (!$this->enabled) {
            return false;
        }
        // @codeCoverageIgnoreEnd
        if (!$this->inloop) {
            return false;
        }
        $data = ob_get_contents();
        ob_clean();
        $this->loopdata[$this->inloop]->appendData($data);
        $this->loopdata[$this->inloop]->appendCallback($callback);
        return true;
    }

 protected function _startcallback(CacheAbstract $cache)
 {
     $key = new CacheKey("startcallback", 1);
     $cache->clean($key);
     $this->assertFalse($cache->start($key));
     echo "something ";
     $this->assertTrue($cache->appendCallback('callbackTesterStart'));
     echo " otherthing";
     $output = $cache->end(false);
     $this->assertContains(CALLBACKVALUE, $output);
     // run again, we should have another value
     $second = $cache->start($key, null, false);
     $this->assertNotFalse($second);
     $this->assertContains(CALLBACKVALUE, $second);
     $this->assertNotEquals($second, $output);
 }