@SimonClark no problem. and welcome to the world of jscad development.
so, each of the packages are managed via 'lerna'. lerna is kind of cool because it automatically detects the dependencies and links everything together during the 'bootstrap' phase.
once everything is linked together, then you can make changes to any of the code, and rerun tests, or run CLI / WEB.
also, each of the packages can be tested individually. for example, you can change directories to packages/modeling, and run the tests using 'npm test'.
if there's too much noise then you can move the *.test.js files into a temporary directory, and test something special by creating another *.test.js file.
AVA is the test harness of choice. It's cool.