The law which mentions the requirements you have to fulfil for German citizenship is StAG §10 https://www.gesetze-im-internet.de/rustag/__10.html
As an acknowledged refugee you can apply for German citizenship after you stay 6 years in Germany. The duration of your asylum procedure also adds to this six years.
After this times and if you fulfil some other requirements you can get through the test to get your German citizenship. In your case I assume, that you will be entitled to apply in July 2020 for your citizenship.
It is advised to ask your local Stadt-, Kreisverwaltung or Ausländerbehörde where you have to apply for passing the Einbürgerungstest.
Is there anything else you need to know?