Providing undefined as a string

[vincentorback]

Fix #22

This resolves the issues I was testing in #22 where an undefined variable broke other plugins by providing an undefined variable instead of a variable with the value of "undefined".

Don’t really know what tests to add because the output will be the same in this plugin context. But if you have an idea I could add something! 👍

[MadLittleMods]

@vincentorback Thanks for the PR 😀

The output string will be the same but we can look ast tree and check the type of the value on that node.

var chai = require('chai');
var expect = chai.expect;

var postcss = require('postcss');
var cssvariables = require('postcss-css-variables');

var fs = require('fs');

var mycss = fs.readFileSync('input.css', 'utf8');

describe('postcss-css-variables', function() {
  it('Should use string values for `undefined` values, see #22', function() {
    return postcss([
        cssvariables(/*options*/)
      ])
      .process(mycss)
      .then(function(result) {
        var root = result.root;
        var fooRule = root.nodes[0];
        expect(fooRule.selector).to.equal('.foo');
        var colorDecl = fooRule.nodes[0];
        expect(colorDecl.value).to.be.a('string');
      });
  });
});

[MadLittleMods]

// Set 'undefined' value as a string to avoid making other plugins down the line unhappy
// See #22

[vincentorback]

Updated with new undefined check + new comment!
What was the extra whitespace you commented on?

[MadLittleMods]

@vincentorback You can expand the past dismissed comments.

Let's add in the test I mentioned earlier.

[vincentorback]

I added a test but I’m really new to mocha so take a look if I should change something.

[MadLittleMods]

I didn't have this in my snippet but lets also add a expect(colorDecl.value).to.be.equal('undefined');

[MadLittleMods]

After fixing up these last points, squash down the commits please

[vincentorback]

I think that’s it!

[MadLittleMods]

@vincentorback Thanks for sorting out the last bits. Will take a look soon 😀

[MadLittleMods]

@vincentorback This has been merged in and released in v0.6.0 and published on npm. Thanks again for the contribution 💞