How to use Node.js global variable in mocha tests

I have found a solution that works for me by using Mocha hooks to set global variable just for testing:

// setup.test.js
import MyFunc from '../helpers/my-func'

before((done) => {
  MyFunc.then((variable) => {
    global.variable = variable
    done()
  })
})

We can use the global.variable in the test just like in the real code.