use() function only returns plugin first time

[ramicohen303]

Related to #1569

I have multiple test files, each loading its own copy of chai and chai-http plugin. The first file works fine, all others fail. If I comment out the first file, the second file works fine, all others fail.

Looking at the code, I believe the issue cause is in chai.js, in the "use" function. The "used" array is global, and once a plugin is added to it, it cannot be added again. However, the exports object is instantiated on every call, but only the first instance gets the plugin.

For now, I created a factory function that returns a singleton chai and chai-http, and I use it in every test file. However, I believe this should be fixed properly.

[koddsson]

@ramicohen303; could you write up a quick failing test in pseudo code for this? It would be helpful so we can make sure we are fixing the correct thing.

[jdmarshall]

There’s an old trick with custom matchers where you create a separate test file that only had a before clause and you wire up the matchers there. I wonder if that would be a useful workaround here.

[jdmarshall]

I’m willing to work on this but I still don’t understand the problem.

if (!~used.indexOf(fn)) {
  fn(exports, util);
  used.push(fn);
}

return exports;

Seems like that returns the correct results every time. I don’t understand why your multiple use scenario wouldn’t work.

I haven’t seen this problem with sinon-chai or chai-as-promised. Something tells me perhaps your http addon is the issue?

[43081j]

because use returns a namespace-like object, and that is the object which plugins can mutate.

so if you have two test files which both do this:

import * as chai from 'chai';
import {fn} from './shared-lib.js';

chai.use(fn);

the fn is the same function in both files, so chai will not call it again, and will not push it into used (since its already there)

but the exports object chai mutates is unique to each test file, so every file after the first one will not call fn again.

in a well designed chai plugin, this is ok, because the plugin should mutate prototypes and such (i.e. stuff that exists across all files).

the only place this will fall over is if a plugin tries to mutate exports itself (tracked in #1569 )