Since you are a wrapper on top of OpenCascade, I assume you have the ability to export STEP solids, and so one potential test you could run is have a series of standard objects that are exported and then re-imported with the basic opencascade tools and then measure the volume of the solid, verifying a solid volume to some small epsilon. This type of volume/mass verification is used in a lot of CAD modeling competitions to determine if a part has been correctly modeled; if the part is of sufficient complexity (especially things involving fillets), the odds that the solid is computed with the correct volume, down to several decimal places, while something else in the modeling is wrong, are astronomically small.