Adjust test script

package.json

@@ -9,7 +9,7 @@
     "lint": "eslint ./",
     "pretest": "npm run lint",
     "test": "npm run unit-test",
-    "unit-test": "istanbul cover --dir reports/coverage node_modules/mocha/bin/_mocha tests/**/*.js"
+    "unit-test": "istanbul cover --dir reports/coverage node_modules/mocha/bin/_mocha tests/lib/**/*.js tests/util/**/*.js tests/index.js"
   },
   "files": [
     "LICENSE",