Best way to get Jest to recompile source code before testing

My code requires npm run-script build to be run, which does node make.js which is a completely custom build script as if you were using grunt or something (but I'm not using any tools). How do I get Jest to --watch and at the same time recompile my build before it runs the tests? Right now I have to have a separate terminal window open, run npm run-script build, and then jest picks up the file change and runs, but I wish it could be automatic.