String diffs not shown anymore when using node assert.equal

[mantoni]

I created a gist that reproduces the issue for me on OS X with node 0.10.32:
https://gist.github.com/mantoni/e2927ced1484f01b1fb8

Thanks for looking into it!

[a8m]

I'm not sure what do you mean by saying "anymore", in which version it works @mantoni ?
as far as I know, you can't get this using assert. for this reason.

[mantoni]

Can't say exactly when it stopped working, but I took this screenshot once: https://www.npmjs.com/package/consolify

[mantoni]

Thanks for the pointer @a8m, I removed the err.showDiff && part from the conditional in the line you mentioned and then it works perfectly fine.

[a8m]

kk, I'm on it.
trying to detect in which version it's stop to work.

update: v1.21.5
this commit: a5d7240

[a8m]

Thanks for pointing that out @mantoni.

[a8m]

Is this something that we want to fix @mochajs/mocha ? if so, I'll label it as a "bug", and start to working on it.

[dasilvacontin]

So it depends on whether the asserting library sets showDiff to true or not, right? Like, as an user, could you do something to show the diff, without modifying the library?

[mantoni]

It's a feature that is advertised on the mocha page, but it only works in specific setups. So if this is not going to considered a bug, it could be a new flag to opt in and it would be nice to pit some notes on how to get it working on the web page.

[a8m]

Yes, but it's worked before (<1.21.5) @dasilvacontin . that's the reason I see it as a regression.

[dasilvacontin]

Could you please answer my doubts/questions?

Regarding if it's a regression or not, we are making people waste time trying to figure out why the diff is no longer showing, and how to make it show it again. That's something I would only do in a major version.

We need to get this fixed this asap.

[a8m]

So it depends on whether the asserting library sets showDiff to true or not, right?

Yes.

Like, as an user, could you do something to show the diff, without modifying the library?

If you're using assert, I don't see any other way except this:

try {
  assert.equal("foo", "bar")
} catch(e) {
  e.showDiff = true
  throw e
}

[dasilvacontin]

Thanks very much, @a8m.

Ugh, this is ugly. Maybe we could add a flag for ignoring .showDiff. Or what would you suggest?

This is not a common case, right? I wouldn't make it the default behavior to ignore .showDiff.

[a8m]

Maybe we could add a flag for ignoring ...

Flag is not a good solution for some reasons(e.g: you can't use it dynamically or for a specific assertions).

I think it should .showDiff by default and if you don't want it, you should explicitly set it to false, like this (and it will not break anything).

[dasilvacontin]

But then the user wouldn't have a choice, it would be up to the assertion module/library, right?

[mantoni]

I like what @a8m proposed because it makes Mocha work as advertised without breaking other libraries that depend on the showDiff property. The proposal brought up by @dasilvacontin make sense and I think having an option to control the behavior would certainly improve the feature. However, I don't see that being necessary to fix the issue.

[a8m]

However, I don't see that being necessary to fix the issue.

Me neither.

[dasilvacontin]

Goes. 🚢

[a8m]

Thanks guys @mantoni @dasilvacontin
fixed in #1626

[arve0]

For other goofer like me, remember that npm test runs local node_modules/mocha. So do a npm install -g mocha if you use mocha mytest.js.