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()

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']