Mocha is able to generate a code coverage report with a little help from JSCoverage . Install JSCoverage for your environment from http://siliconforks.com/jscoverage/. JSCoverage will parse source code and generate an instrumented version; this enables mocha to execute this generated code and create a report. We will need to update ./app.js.

module.exports = (process.env['NODE_ENV'] === "COVERAGE")
 ? require('./lib-cov/express')
 : require('./lib/express'),

JSCoverage takes as arguments an input directory, and an output directory:

jscoverage lib lib-cov

Depending on your version of JSCoverage, you may need to add the –no-highlight switch:

jscoverage lib lib-cov --no-highlight

The following command will generate the coverage report, as shown in the following screenshot:

NODE_ENV=COVERAGE mocha -R html-cov > coverage.html