How to unit test a Node.js module that requires other modules and how to mock the global require function?

Question

This is a trivial example that illustrates the crux of my problem:

var innerLib = require(\'./path/to/innerLib\');

function underTest() {
    return innerLi         


        

Answer 1

Mocking require feels like a nasty hack to me. I would personally try to avoid it and refactor the code to make it more testable. There are various approaches to handle dependencies.

1) pass dependencies as arguments

function underTest(innerLib) {
    return innerLib.doComplexStuff();
}

This will make the code universally testable. The downside is that you need to pass dependencies around, which can make the code look more complicated.

2) implement the module as a class, then use class methods/ properties to obtain dependencies

(This is a contrived example, where class usage is not reasonable, but it conveys the idea) (ES6 example)

const innerLib = require('./path/to/innerLib')

class underTestClass {
    getInnerLib () {
        return innerLib
    }

    underTestMethod () {
        return this.getInnerLib().doComplexStuff()
    }
}

Now you can easily stub getInnerLib method to test your code. The code becomes more verbose, but also easier to test.