I have a simple test case in mocha but it gives very different results:

A. Vanilla Code runs fine!

const body: string = `
            var moment = require('moment');
            setInterval(function(){
                console.log(moment().unix());
            }, 2000)
        `
const vm = new NodeVM({
    console: 'redirect',
    require: {
           external: true,
                root: process.cwd()
            }
     })
vm.run(body)
vm.on('console.log', function(consoleMessage){
      console.log('from event', consoleMessage)
})

B. In this Mocha Script, I get a new error

describe('Vanilla Script Test', function () {
    it('should return a console log of a unix from moment', function (done) {
        const body: string = `
            var moment = require('moment');
            setInterval(function(){
                console.log(moment().unix());
            }, 2000)
        `
        const vm = new NodeVM({
            console: 'redirect',
            require: {
                external: true,
                root: process.cwd()
            }
        })
        vm.run(body)
        vm.on('console.log', function(consoleMessage){
            done()
        })
    })
})

C. The new error, that only happens in Mocha

VMError: You must specify script path to load relative modules.