This tests API from http://goqr.me/api/
Test are far from exhaustive, but is easy to make an idea of how to test parameters and how to test more complex combinations of parameters.
To test data contained inside QR, the API itself is used (Read QR). Also, to test colors and background colors, results are tested against samples stored in resources folder, pixel by pixel.
To test this API, I used TestNG and gradle to manage dependencies.
In a console, at the root of the project simply type
./gradlew test --rerun-tasks