chai-changes

chai-changes

chai-changes is an extension to the chai assertion library that provides a set of change-specific assertions.

Usage

Include chai-changes.js in your test file, after chai.js (version 1.0.0-rc1 or later):

<script src="chai-changes.js"></script>

Use the assertions with chai's expect or should assertions.

Assertions

All assertions use a when mechanism.

Using 'expect':

expect(-> codeThatYieldsAChangedResult).to....when ->
  executeTheCodeThatCausesTheChange()

The code within the expect section will be executed first, then the code in the when section will be executed and then the code in the expect section will be executed again and the differences will be asserted.

Same test using 'should':

(-> codeThatYieldsAChangedResult).should....when ->
  executeTheCodeThatCausesTheChange()

when

Executes the build up pre- and post-conditions. First it executes the pre-conditions, then it will execute the provided callback. And after the callback it will assert the post-conditions. It will change the object in the assertion chain to the result of the callback.

When the callback returns a promise, the post-conditions are executed when the promise is fulfilled.

Since the 'object' in the assertion chain is changed after the when, you can chain chai-as-promised matchers too, like: (-> result).should.change.to(4).when(-> object.methodThatReturnsPromise()).and.notify(done)

This makes this mechanism also compatible with mocha-as-promised

change

Assert if the 'expect/should' changes its outcome when 'when' is executed

result = 0
(-> result).should.change.when -> result += 1
expect(-> result).to.change.when -> result -= 1
expect(-> result).not.to.change.when -> result = result * 1

change.by(delta)

Assert if the change of the 'expect/should' has the provided delta

result = 0
(-> result).should.change.by(3).when -> result += 3
expect(-> result).not.to.change.by(-3).when -> result += 1
expect(-> result).to.change.by(-2).when -> result -= 2

change.from(startValue)

Assert if the change starts from a certain value. The value is compared using a deep equal.

result = ['a', 'b']
(-> result).should.change.from(['a', 'b']).when -> result.push('c')
(-> result).should.change.from(['a', 'b']).to(['a', 'b', 'c']).when -> result.push('c')

change.to(endValue)

Assert if the change ends in a certain value. The value is compared using a deep equal.

result = ['a', 'b']
(-> result).should.change.to(['a', 'b', 'c']).when -> result.push('c')
(-> result).should.change.from(['a', 'b']).to(['a', 'c']).when -> result = ['a', 'c']

License

Copyright (c) 2012 Matthijs Groen

MIT License (see the LICENSE file)