"Combinators goes assertion" (or was it the other way round?)
If you need to work in referee too then you should get the one from github, NOT the one on npm. Like so:
git clone https://github.com/busterjs/referee-combinators.git
cd referee-combinators
mkdir node_modules
git clone https://github.com/busterjs/referee.git node_modules/referee
npm install
cd node_modules/referee
npm install
cd ../..
PATH=`pwd`/node_modules/.bin:$PATH