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Mocha + Istanbul + CLI

This example shows how to use Babel in conjunction with Mocha and Istanbul. It allows you to run the tests by themselves, but also to run them with code coverage.

Installation

  1. Clone this repository
  2. Navigate to this directory via cd examples/mocha-istanbul-cli
  3. Install the npm dependencies via npm install

Running the scripts

To run the tests, run npm test. For code coverage, run npm run coverage.

How it works

For a description of the npm test command, refer to the mocha-cli example. The script here is identical to the one in that example.

What's new to this example is the npm run coverage script. I'd love to walk through it step-by-step with you, but I'd be lying if I said I understood exactly how it works. I'll do my best and explain what I do know, though.

The first thing you might be wondering is...where's Instanbul? This example does use Istanbul, just indirectly. isparta is a wrapper for Istanbul that allows us to write ES2015 code.

Back to the command. It starts off with babel-node, which is a tool provided by Babel. What it does is automatically transpile any subsequent scripts run in Node.

The script that we execute is node_modules/.bin/isparta. The directory node_modules/.bin is provided to us by npm: it's a collection of all of the executables in the locally-installed node_modules.

This tells babel-node to execute isparta's executable.

Next up is cover. This seems to be an API that isparta inherited from istanbul.

The last piece is _mocha, which users of istanbul will know differs from the standard istanbul CLI. What this is is a reference to the _mocha executable from the mocha npm package. Did you know that such a thing existed? As a consumer of mocha, and not a maintainer, I did not before using isparta.

We can see from the repository that mocha's main , mocha, is a small wrapper around the _mocha executable, which does most of the heavy lifting.

isparta only works with _mocha, and not mocha. Why? I'm not sure. That's what I meant about not fully understanding this command. I learned how to do this from the isparta documentation, but the docs do go into much depth as to why it must work this way.

I'd love to elaborate further on how this command works. Got any ideas? Please let me know by opening an issue!

.babelrc

There's one last important detail that makes all of this work: the .babelrc file. Our configuration in that file tells Babel that we want to transpile ES2015 code into ES5 code. This is necessary because Babel makes no assumptions about how you want to transform the code as of v6.

A note on Chai

These examples all use Chai as the assertion library for the tests. It should be relatively straightforward to swap it out for your assertion library of choice, which is why I haven't included other examples. If you're having trouble, raise an issue and I'll be glad to help out.