I went to go test an SVG using your checker, and it was unable to locate the font I used (Carlito), despite that font being listed as installed on Wikimedia (as shown here: https://meta.wikimedia.org/wiki/SVG_fonts).

Luckily, I remembered that File:Test.svg exists, and tried it there, and it worked just fine. However, I believe the goal of your SVG Checker is to not have to use Test.svg.