Running mocha tests in parallel

Mocha by design runs tests in series. Often this is not efficient and you might want to run some or all of the tests in parallel.

Mocha uses a wrapper executable under the hood, which runs the “real” _mocha executable. The _mocha executable is run via require('child_process').spawn. See bin/mocha. This makes it easy to run tests in parallel, in their own child processes with their own environment. We had success in two scenarios: i). inspecting the content of the files for the presence of a function and choosing whether to run them in parallel or series and ii). running a selenium suite multiple times with different environment variables specifying different browser configurations.

Feel free to use the script below to make your own runner. It is heavily inspired by bin/mocha.

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Originally published at https://msyea.github.io on June 5, 2019.