Sinon: Stub a function for only one argument

[gyandeeps]

So basically I have an function whose behavior I want to stub only if the argument is equal to something.
Example

var foo = {
    bar: function(arg1){
        return true;
    }
};

var barStub = sinon.stub(foo, "bar");
barStub.withArgs("test").returns("Hi");

// Expectations
console.log(foo.bar("test")); //works great as it logs "Hi"

// my expectation is to call the original function in all cases except 
// when the arg is "test"
console.log(foo.bar("woo")); //doesnt work as it logs undefined

[mroderick]

I am having a hard time imagining when I would need such functionality.

Do you have a less synthetic example that might make me understand the need for this?

[gyandeeps]

In my use case, i have one function which reads files. So I wanted to fake the response when it tries to read file xxxx.txt but for all the rest I want the function to behave as it is.

Now in Jasmine they have callThrough function which allows you to call the original function.

[gyandeeps]

Same as https://github.com/cjohansen/Sinon.JS/issues/735

I guess we can close this as we know the answer.

[mroderick]

I guess we can close this as we know the answer.

Yeah. From your use case it sounds like your function has more than one responsibility.

[mocheng]

Even tough this issue is closed, I just want to post my case to prove it is necessary.

In my case, the program is run with babel-register and there is one unit test need to stub readFileSync for given filename and proxyquire to stub required module. However, babel-register would find .babelrc and parse it during execution. As a result, below code will fail.

      stub(fs, 'readFileSync').withArgs(givenPath).returns(JSON.stringify(h3oConfig));
      const foo = proxyquire('./foo', stub); // this will fail on reading .babelrc

It sounds that stub would better to have only customized returned value on given args.

[mantoni]

@mocheng You can program the stub to have different behavior for different arguments like this:

stub(fs, 'readFileSync')
fs.readFileSync.withArgs(givenPath).returns(JSON.stringify(h3oConfig));
fs.readFileSync.withArgs('.babelrc').returns('#');

[mocheng]

@mantoni Thanks.
It just looks tedious to mock .babelrc and my .babelrc has quite a lot of stuff.
Now, I just totally rely on proxyquire for this case.

[mantoni]

@mocheng There is a new feature that just landed on master which allows to call through to the original implementation. It's not in a release yet, and it will only be supported in Sinon 2. You can point your dependency to master for now.

[mocheng]

@mantoni cool. thanks!