How to mock dependencies for unit tests with ES6 Modules

Question

I'm trying to fiddle with Ecmascript 6 modules using webpack + traceur to transpile to ES5 CommonJS, but I'm having trouble successfully unit testing them.

I tried using Jest + traceur preprocessor, but the automocking and dependency names seem to get screwy, plus I can't seem to get sourceMaps to work with Jest and node-inspector debugging.

Is there a better framework to unit test ES6 modules?

Answer 1

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 can't speak for traceur which was the framework used in the question, but I've found this to work with my setup of Karma, Jasmine, and Babel, and I'm posting it here as this seems to be the most popular question of this type.

I've used this strategy most often when needing to mock Redux actions. Here's a short example:

import * as exports from 'module-you-want-to-mock';
import SystemUnderTest from 'module-that-uses-above-module';

describe('your module', () => {
  beforeEach(() => {
    spyOn(exports, 'someNamedExport');  // mock a named export
    spyOn(exports, 'default');          // mock the default export
  });
  // ... now the above functions are mocked
});