Is there any way to stub these type of functions?

Question

There is a file helperFunction.js, which looks like:

module.exports = (arg1, arg2) => {
   \\function body
}

Now, in file.js, this function can be simply called by:

let helperFunction = require('./helperFunction.js');

//some code here

let a=1, b=2;

let val = helperFunction(a,b);

//some code here 

In order to test file.js, I want to stub the helperFunction. However, the syntax for sinon.stub looks like:

let functionStub = sinon.stub(file, "functionName");

And here in my case the fileName itself is the function name. How do I create a stub for helperFunction now? Or is there anything else I can do?

Answer 1

You can use a library like proxyquire which can be used to override dependencies during testing.

That would mean you would end up with something like this:

const helper = sinon.stub();

const moduleToTest = proxyquire('./your-file-name’, {
  './helperFunction': helper,
});

Although if you do not want to add a new library, you can always switch to refactoring the helperFunction.js file and exporting your function as a named export instead of default export. That will give you an object having the method you need to stub and that would fit in nicely with your current approach