How can I mock the imports of an ES6 module?

I've started employing the import * as obj style within my tests, which imports all exports from a module as properties of an object which can then be mocked. I find this to be a lot cleaner than using something like rewire or proxyquire or any similar technique. I've done this most often when needing to mock Redux actions, for example. Here's what I might use for your example above:

import * as network from 'network.js';describe("widget", function() {  it("should do stuff", function() {    let getDataFromServer = spyOn(network, "getDataFromServer").andReturn("mockData")    let widget = new Widget();    expect(getDataFromServer).toHaveBeenCalledWith("dataForWidget");    expect(otherStuff).toHaveHappened();  });});

If your function happens to be a default export, then import * as network from './network' would produce {default: getDataFromServer} and you can mock network.default.

carpeliam is correct, but note that if you want to spy on a function in a module and use another function in that module calling that function, you need to call that function as part of the exports namespace, otherwise the spy won't be used.

Wrong example:

// File mymodule.jsexport function myfunc2() {return 2;}export function myfunc1() {return myfunc2();}// File tests.jsimport * as mymoduledescribe('tests', () => {    beforeEach(() => {        spyOn(mymodule, 'myfunc2').and.returnValue = 3;    });    it('calls myfunc2', () => {        let out = mymodule.myfunc1();        // 'out' will still be 2    });});

Right example:

export function myfunc2() {return 2;}export function myfunc1() {return exports.myfunc2();}// File tests.jsimport * as mymoduledescribe('tests', () => {    beforeEach(() => {        spyOn(mymodule, 'myfunc2').and.returnValue = 3;    });    it('calls myfunc2', () => {        let out = mymodule.myfunc1();        // 'out' will be 3, which is what you expect    });});

vdloo's answer got me headed in the right direction, but using both CommonJS "exports" and ES6 module "export" keywords together in the same file did not work for me (Webpack v2 or later complains).

Instead, I'm using a default (named variable) export wrapping all of the individual named module exports and then importing the default export in my tests file. I'm using the following export setup with Mocha/Sinon and stubbing works fine without needing rewire, etc.:

// MyModule.jslet MyModule;export function myfunc2() { return 2; }export function myfunc1() { return MyModule.myfunc2(); }export default MyModule = {  myfunc1,  myfunc2}// tests.jsimport MyModule from './MyModule'describe('MyModule', () => {  const sandbox = sinon.sandbox.create();  beforeEach(() => {    sandbox.stub(MyModule, 'myfunc2').returns(4);  });  afterEach(() => {    sandbox.restore();  });  it('myfunc1 is a proxy for myfunc2', () => {    expect(MyModule.myfunc1()).to.eql(4);  });});