Leaflet AJAX Map FitBounds

I am searching for a solution to fit a leaflet map's bounds to display the content of a loaded geoJSON file.

For loading the file I use leaflet-ajax. I tried already this, but I have no idea how I can get the layer's bounds. Any Suggestions how I can adjust the displayed map sector to display the geoJSON file? Thanks.

var geojsonLayer = new L.GeoJSON.AJAX('http://localhost:8080/test.geojson');
geojsonLayer.addTo(this.map);
this.map.fitBounds(geojsonLayer.getBounds());