alexjeffburke / cup-of-unexpected

cup-of-unexpected

A reimplementation of the chaijs.expect interface using Unexpected.

This module intends to be a drop-in replacement for projects using the expect() interface of the Chai Assertion Library. The set of supported assertions is close both in terms of API and behaviour as is possible.

Getting started

Take the following test suite:

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

describe('add', function() {
  it('should return a number', function() {
    var result = add(1, 2);
    expect(result).to.be.a('number');
  });

  it('should add to numbers correctly', function() {
    var result = add(2, 2);
    expect(result).to.eql(3);
  });
});

With cup-of-unexpected installed:

$ npm install --save-dev expect-the-unexpected

Switching the test suite over is as simple as:

-var chai = require('chai');
+var chai = require('cup-of-unexpected');

Any tests you're written will continue to execute unchaged.

Unsupported features

The primary functionality that we do not currently support is plugins.

Custom Assertions

While chai plugins are not suported the library does support the use of Unexpected plugins. These are implemented differrently and are localised to an instance of expect being used to avoid having any extensions bleed over into other parts of the test suite.

Let's use an example of an assertion intended to be used in the browser to check whether a particular DOM node has a CSS class. We can implement this using the Unexpected assertion syntax and add it directly via the fully compatible addAssertion() API:

expect.addAssertion('[not] to have css class', function(
  expect,
  subject,
  value
) {
  var $element = $(subject);
  var elementClasses = ($element.attr('class') || '').split(' ');
  expect(elementClasses, '[not] to contain', value);
});

The assertion can then be used like any other expect assertion by using its dotted path name:

var html = '<div class="foo bar baz"></div>';

expect(html).to.have.css.class('foo');

License

This module is published under the ISC license. See the LICENSE file for details.