code-coverage.md

Code coverage

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As AVA spawns the test files, you can't use istanbul for code coverage; instead, you can achieve this with nyc which is basically istanbul with sub-process support.

Setup

First install NYC:

$ npm install nyc --save-dev

Then add both the .nyc_output and coverage directories to your .gitignore file.

.gitignore:

node_modules
coverage
.nyc_output

ES5 coverage

Using NYC to provide coverage for production code written in ES5 is simple. Just prepend your test script with nyc:

{
	"scripts": {
		"test": "nyc ava"
	}
}

That's it!

If you want to create HTML coverage reports, or upload coverage data to Coveralls, you should skip down to those sections below.

ES2015 coverage

Using Babel to transpile your production code is a bit more involved. Here we've broken it down into multiple steps.

Configure Babel

First, we need a Babel configuration. The following is just an example. You will need to modify it to fit your needs.

package.json:

{
	"babel": {
		"presets": ["es2015"],
		"plugins": ["transform-runtime"],
		"ignore": "test.js",
		"env": {
			"development": {
				"sourceMaps": "inline"
			}
		}
	}
}

There are two important things to note from the example above.

1. We ignore test files because AVA already handles transpiling tests for you.

2. We specify inline source maps for development. This is important for properly generating coverage. Using the env section of the Babel configuration allows us to disable source maps for production builds.

Create a build script

Since it is unlikely you want inline source maps in your production code. You should specify an alternate environment variable in your build scripts:

package.json

{
	"scripts": {
		"build": "BABEL_ENV=production babel --out-dir=dist index.js"
	}
}

WARNING: BABEL_ENV=production does not work on Windows, you must use the set keyword (set BABEL_ENV=production). For cross platform builds, check out cross-env.

Note that the build script really has very little to do with AVA, and is just a demonstration of how to use Babel's env configuration to manipulate your config so it's compatible with AVA.

Use the Babel require hook

To use the Babel require hook, add babel-core/register to the require section of you AVA config in package.json.

{
	"ava": {
		"require": ["babel-core/register"]
	}
}

Putting it all together

Combining the above steps, your complete package.json should look something like this:

{
	"scripts": {
		"test": "nyc ava",
		"build": "BABEL_ENV=production babel --out-dir=dist index.js"
	},
	"babel": {
		"presets": ["es2015"],
		"plugins": ["transform-runtime"],
		"ignore": "test.js",
		"env": {
			"development": {
				"sourceMaps": "inline"
			}
		}
	},
	"ava": {
		"require": ["babel-core/register"]
	}
}

HTML reports

NYC creates a json coverage file for each forked process in the .nyc_ouput directory.

To combine those into a human readable HTML report, do the following:

$ ./node_modules/.bin/nyc report --reporter=html

Or, use an npm script to save on typing:

{
	"scripts": {
		"report": "nyc report --reporter=html"
	}
}

This will output a HTML file to the coverage directory.

Hosted coverage

Travis CI & Coveralls

First, you must login to coveralls.io and activate your repository.

Once that is done, add coveralls as a development dependency:

$ npm install coveralls --save-dev

Then add the following to your .travis.yml:

after_success:
	- './node_modules/.bin/nyc report --reporter=text-lcov | ./node_modules/.bin/coveralls'

Your coverage report will then appear on coveralls shortly after Travis completes.