[removed] Mocking Constructor using Sinon

Question

I am pulling my hair out trying to figure out how to mock a constructor using sinon. I have a function that will create multiple widgets by calling a constructor that accepts a

Answer 1

Using Sinon 4.4.2, I was able to mock an instance method like this:

const testObj = { /* any object */ }
sinon.stub(MyClass.prototype, "myMethod").resolves(testObj)
let myVar = await new MyClass(token).myMethod(arg1, arg2)
// myVar === testObj

A similar solution provided here: Stubbing a class method with Sinon.js

Answer 2

I was able to get StubModule to work after a few tweaks, most notably passing in async:false as part of the config when requiring in the stubbed module.

Kudos to Mr. Davis for putting that together

Answer 3

I ran into this error by mistakenly typing sinon.stub.throws(expectedErr) rather than sinon.stub().throws(expectedErr). I've made similar mistakes before and not encountered this particular message before, so it threw me.

Answer 4

Use sinon.createStubInstance(MyES6ClassName), then when MyES6ClassName is called with a new keyword, a stub of MyES6ClassName instance will returned.

Answer 5

I needed a solution for this because my code was calling the new operator. I wanted to mock the object that the new call created.

var MockExample = sinon.stub();
MockExample.prototype.test = sinon.stub().returns("42");
var example = new MockExample();
console.log("example: " + example.test()); // outputs 42

Then I used rewire to inject it into the code that I was testing

rewiredModule = rewire('/path/to/module.js');
rewiredModule.__set__("Example", example);

Answer 6

Just found this in the documentation.

If you want to create a stub object of MyConstructor, but don’t want the constructor to be invoked, use this utility function.

var stub = sinon.createStubInstance(MyConstructor)