mongoose.connect(), first argument should be String, received undefined

mongoose mocha.js

I think you miss importing env file.

require('dotenv').config({ path: 'ENV_FILENAME' });

mongoose mocha.js

To read from .env file you have to install dotenv ( npm i dotenv / yarn add dotenv)and then just add this on top of your file.

const dotenv = require("dotenv");dotenv.config();

mongoose mocha.js

I was also facing same problem after add code { useNewUrlParser: true } in mongoose.connect() method. Problem resolved.

mongoose.connect(config.DB,{ useNewUrlParser: true }));

CodeHunter