`returns` clears fake's `callArgAt`

[fpascutti]

Describe the bug
Starting from sinon@17.0.1, using returns clears fake's callArgAt.
This means that the callback will not be called.

To Reproduce
Run the following:

const sinon = require("sinon");
const assert = require("assert");

const stub = sinon.stub();
stub.callsArgWith(0, "Hello").returns("World");

const cb = sinon.stub();
const ret = stub(cb);

assert.strictEqual(ret, "World");
assert(cb.calledOnce);
assert.deepEqual(cb.firstCall.args, ["Hello"]);

Expected behavior
The callback should be properly invoked.

Context (please complete the following information):

• Library version: 17.0.1
• Environment: Windows / Node.JS

Additional context

Bug introduced by the fix for #2566 (see #2567).
Might be fixed by removing this line but this needs validation.

+@rluvaton

[rluvaton]

Will try to create a fix later today

But what do we define the behavior should be?

Should returns only override the things that affect returning/throwing values?

[rluvaton]

Unfortunately, I won't be able to get to that soon, do you want to create a PR to fix it?

[zmknox]

I seem to be experiencing this same bug, but in reverse. I have a .returns() followed later by a callsArgWith(), and the callsArgWith is clearing the return, breaking my tests.

In terms of what the behavior should be, I feel like there isn't really a conflict here. I don't see any reason that the stub couldn't both call one of its args and return some value.

[fatso83]

Yeah, no conflict AFAI can see either. This should be a really small fix, if someone is interested in getting it working. Just remember to document it using a regression test 😉

[fatso83]

Should be fixed by #2593