How to return fake data from spy.on(obj, 'funcName') when called ?

[narainsagar]

I don't know is there any function or not!
Please let me know is it possible?

Something like that:
spy(obj, 'funcName').and.returnValue(5); // spy will return a fake data when called`

[scaljeri]

+1 I would really like to know this too!

[lucasfcosta]

Hello guys, thanks for the issue!
For what I can see chai-spies is not able change the return value of a function. Chai's focus is actually doing assertions, so you can only run things related to assertions on spies.
To create stubs for your functions you can use SinonJS.

---

EDIT: I'm not sure if I totally understand your doubt, but I was reading this again and actually we have this:

    /**
     * # chai.spy.returns (function)
     *
     * Creates a spy which returns static value.
     *
     *      var method = chai.spy.returns(true);
     *
     * @param {*} value static value which is returned by spy
     * @returns new spy function which returns static value
     * @api public
     */

I hope it is what you guys were looking for.

[keithamus]

Hey @narainsagar @scaljeri and @lucasfcosta 😄

Right now the spy.on API doesn't allow you to override the functionality. Some discussion has gone on about this in #38 (see #38 (comment)). The alternatives so far are:

Array.prototype.push = chai.spy(function () { return undefined });
Array.prototype.push = chai.spy.returns(undefined);
Array.prototype.push = function () { return undefined; }
chai.spy.on(Array.prototype, 'push');

We've discussed before about having extra methods on the spy interface, but we'd like to move away from that (#38 has some on this, as does this comment in #35: #35 (comment)).

I'll close this, because it's on the radar and will likely come as a result of #38. If you want to help out, continuing the discussion there would be awesome!