writeFileSync stub causing reference error.

[Lukas Wilkeer]

I'm attempt to stub the fs.writeFileSync method, but it's causing a Reference Error.

In that case, oeverloading the fs method causes troubes as sinon.restore() doesn't work.

My stub.

const writeImageStub = sinon.stub(fs, 'writeFileSync')

      .callsFake((file, data, (err) => {

        expect(file).to.be.a('string')

        expect(getFileExtension(data)).to.equal('jpg')

        expect(new Buffer.alloc(data)).to.be.a('object')

        return '/static/images/image.jpg'

      }))

Reference error: file is not defined.

How to do this, what causing this and exist other method?

PS:

Spying the method causes the write operation to be executed, on this case i have to delete the files written, but how to get the filename as the format is filename.Date.now.extension. Don't exist a way to store as a global variable to do this.

[Amresh Yadav]

Hi Lukas,

you can try something like this,

const writeImageStub = sinon.stub(fs, 'writeFileSync').callsFake((file, data, _cb)=>{
    expect(typeof file).toBe('string');
   // expect(getFileExtension(data)).to.equal('jpg')
   // expect(new Buffer.alloc(data)).to.be.a('object')
    fs.writeFile(file,data,_cb)
});
writeImageStub("abc.txt","Hello world",(err, data)=>{
    console.log(err,data);
})

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Regards,
Amresh Yadav

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[Corey Cleary]

`file` and `data` have no value... so that's why you get the ReferenceError. Understanding why you're trying to stub the filesystem method would help (i.e. - what other code are you trying to test that is causing you to need to stub the fs), but from what I can tell given the context here you can simplify this a lot.

.callsFake takes a function, so you can just do this:

const writeImageStub =

  sinon

    .stub(fs, 'writeFileSync')

    .callsFake(() => '/static/images/image.jpg')

What you have is more of a mock than a stub, because you're returning pre-configured data AND attempting to verify behavior as part of the fake. I generally avoid mocks.

Also, you shouldn't need to verify/expect things as part of a core module or even 3rd party modules. You should just verify the code you own. Does that help?