Make assertions (such as .exist) callable

I am currently writing some tests using the expect-version of chai. And it is going fine, except there is a readability issue.

Take the following code:

expect(someVariable).to.exist;

This is perfectly valid, and will test as expected, since the assertion is done inside the getter .exist.

But to my eye, there is no action taken here. I would much prefer the line to be:

expect(someVariable).to.exist();

This can be achieved by simply changing the .exist definition from:

Object.defineProperty(Assertion.prototype, 'exist',
  { get: function () {
      this.assert(
          null != flag(this, 'object')
        , 'expected #{this} to exist'
        , 'expected #{this} to not exist'
      );

      return this;
    }
  , configurable: true
});

to:

Object.defineProperty(Assertion.prototype, 'exist',
  { get: function () {
      this.assert(
          null != flag(this, 'object')
        , 'expected #{this} to exist'
        , 'expected #{this} to not exist'
      );

      var self = this;
      return function() { return self; };
    }
  , configurable: true
});

The only drawback is that you cannot chain directly on .exist (like expect(a).to.exist.ok), but since there is no .and and the tests does not break after doing the change above, I don’t see that as an issue.

So the question is, is this only an issue in my mind? And should I spend time on making a proper pull request?

[mgol]

One problem with this approach is that many editors/linters warns against using expressions as statements. It’s quite useful to not have to disable such settings but sometimes they can only be set per project so one can’t just disable them for tests.

[mgol]

ES6 Proxies are a suitable idea. But we should discuss this in a new issue, rather than continuing discussion here.

Sure. I’ve just created #407 for that.