chore: add test coverage (#4960)

babel.config.js

@@ -24,6 +24,7 @@ module.exports = {
         '@babel/preset-typescript',
       ],
       plugins: [
+        'babel-plugin-istanbul',
         '@babel/plugin-proposal-object-rest-spread',
         '@babel/plugin-syntax-dynamic-import',
         '@babel/plugin-transform-regenerator',