node.js - Sinon stub function used with destructuring

Question

I wish to stub a function used in the file I'm currently testing. This function is required with a destructuring like this:

 const { theFunctionIWant } = require('path/to/module')

When testing, the stub is never called, and the real function proceed to be called. But when I require it 'normally' (i.e: without destructuring)

const myModule = require('path/to/module')

then the stub is correctly used and everything works fine

I sense that it's because of how the destructuring works and the fact that sinon stub the object property and not the function directly. Anyhow if you can provide me some insights I will be grateful !

Answer 1

The reason stubbing the method of the module doesn't work when using destructuring from a dependant module is quite simple and has to do with the time you bind the actual function reference. It doesn't have anything to do with CommonJS modules, Sinon or Node per se, so I'll start out with simple javascript examples.

const stub = (o, method) => (o[method] = () => "I am a stub");

const obj = {
  methodFoo() {
    return "I am foo";
  }
};

// same as doing `const methodFoo = obj.methodFoo;`
const { methodFoo } = obj; // "import" using destructuring

console.log("obj.methodFoo(): ", obj.methodFoo());
console.log("methodFoo()", methodFoo());

console.log("Stubbing out method!");
stub(obj, "methodFoo");

console.log("obj.methodFoo: ", obj.methodFoo());
console.log("methodFoo()", methodFoo());