Add tests coverage

package.json

@@ -28,7 +28,7 @@
     "minify": "uglifyjs $npm_package_main -o $npm_package_main --mangle --compress --source-map",
     "push": "git commit -am $npm_package_version && git tag $npm_package_version && git push && git push --tags && npm publish",
     "release": "npm run push && release --publish",
-    "test": "jest"
+    "test": "jest --coverage"
   },
   "dependencies": {},
   "devDependencies": {