public function assert()
    {
        // fetch data
        $data = $this->fetchData();
        if (!$data) {
            throw new ContentNotFound("Fetched snapshot is empty.");
        }

        $this->load();

        if (!$this->dataSet) {
            $this->printDebug('Snapshot is empty. Updating snapshot...');
            $this->dataSet = $data;
            $this->save();
            return;
        }

        try {
            $this->assertData($data);
            $this->printDebug('Data matches snapshot');
        } catch (AssertionFailedError $exception) {
            $this->printDebug('Snapshot assertion failed');

            if (!is_bool($this->refresh)) {
                $confirm = Debug::confirm('Should we update snapshot with fresh data? (Y/n) ');
            } else {
                $confirm = $this->refresh;
            }

            if ($confirm) {
                $this->dataSet = $data;
                $this->save();
                $this->printDebug('Snapshot data updated');
                return;
            }

            $this->fail($exception->getMessage());
        }
    }