stubbing require's using sinon

test.js

// foo-module.js
module.exports.bar = () => {
  return "hello bar";
};

// my-file.test
const foo = require("./foo-module");
module.exports.myBar = () => {
  return foo.bar();
};

// test.js
const sinon = require("sinon");
const test = require("ava");
const fooModule = require("./foo-module");
const myFile = require("./my-file");

// stubbing module method to return a new value
sinon.stub(fooModule, "bar").returns("goodbye bar");

test("foo-module.bar() should return goodbye bar", t => {
  t.is(fooModule.bar(), "goodbye bar");
});

test("my-file.myBar() should return goodbye bar", t => {
  t.is(myFile.myBar(), "goodbye bar");
});