cheerio/node remote server can only execute keywords written in node.js. Mocha is a unit testing framework itself, which wouldn't lend itself to direct integration with RF for integration.
Your best options:
* rewrite the mocha tests to be node.js function calls wrapped or called by cheerio / node remote server that RF can call. Then do all your assertions via RF not (in node like you did with mocha). The node code would only be to invoke the code under test but not to assert it, assert through RF side.
* run mocha tests "as is" but you call it via RF using OperatingSystemLibrary or SSH/TelnetLibrary calling mocha like a shell call through RF, not invoking node.js code based interfacing. From here, either store return code from mocha into RF variable and use it to validate pass/fail or store the stdout output (or the output files) from mocha test run into variable and then validate pass/fail by regex analysis of the results (does it contain any fail messages, etc.)