The engine is simply tested with the usual ctest, which runs all normal commandline tests using node. There is not much testing of the browser integration yet. The WASM port is usable, but far from perfect. Interactive test are at SWI-Prolog WASM demos, notable Some tests. There is no CI for it. Complete CI is anyway a bit of a problem due to the enormous diversity of environment in which you can compile SWI-Prolog and the various configuration options. So, as yet there is only fully integrated CI for the default build on 64 bit Intel/AMD Ubuntu Linux. In my dev environment I test a lot more configurations after potentially non-portable changes.