add coverage

.babelrc

@@ -1,3 +1,10 @@
 {
   "presets": ["es2015", "es2016", "stage-2"],
+  "env": {
+    "test": {
+      "plugins": [
+        ["__coverage__", {"ignore": "*.+(test|stub).*"}]
+      ]
+    }
+  }
 }

karma.conf.js

@@ -1,5 +1,7 @@
+process.env.BABEL_ENV = 'test'
 const webpackEnv = {test: true}
 const webpackConfig = require('./webpack.config.babel')(webpackEnv)
+
 const fileGlob = 'src/**/*.test.js'
 
 module.exports = config => {
@@ -12,7 +14,14 @@ module.exports = config => {
     },
     webpack: webpackConfig,
     webpackMiddleware: {noInfo: true},
-    reporters: ['progress'],
+    reporters: ['progress', 'coverage'],
+    coverageReporter: {
+      reporters: [
+        {type: 'lcov', dir: 'coverage/', subdir: '.'},
+        {type: 'json', dir: 'coverage/', subdir: '.'},
+        {type: 'text-summary'},
+      ],
+    },
     port: 9876,
     colors: true,
     logLevel: config.LOG_INFO,

package.json

@@ -6,6 +6,7 @@
   "devDependencies": {
     "babel-core": "6.13.2",
     "babel-loader": "6.2.4",
+    "babel-plugin-__coverage__": "11.0.0",
     "babel-preset-es2015": "6.13.2",
     "babel-preset-es2016": "6.11.3",
     "babel-preset-stage-2": "6.13.0",
@@ -18,6 +19,7 @@
     "karma": "1.1.2",
     "karma-chai": "0.1.0",
     "karma-chrome-launcher": "1.0.1",
+    "karma-coverage": "1.1.1",
     "karma-mocha": "1.1.1",
     "karma-webpack": "1.7.0",
     "mocha": "3.0.1",