chai-builder

First Class Expectations

A chai plugin to separate expectations from the the values they are tested on.

var expect = require('chai').expect;
var should = require('chai-buider/use');
 
var expectation = should.equal(4);
expectation.test(4);
expect(4).to.equal(4);

This example shows the correspondence beetween the expect syntax and should builder syntax. This extends to all of chai’s language properties—so in general the following are equivalent.

should.a.b.c.test(target);
expect(target).a.b.c
 
should.a.b.f(x, y).test(target);
expect(target).a.b.f(x,y)

Expecation also have a label property that describes the expectation

should.be.defined.and.equal(4).label
// -> 'should be defined and equal 4'

Use Cases

Building custom expecations.

var shouldHaveAddress =
  should.have.property('address')
        .as.an('object')
        .and.with.key('name')
var shouldHaveExtendedAddress = 
  shouldHaveAddress.with.key('street').and.key('city')
 
shouldHaveAddress.test({address: {name: 'Willy'}})
shouldHaveExtendedAddress.test({address: {
  name: 'Willy',
  street: 'Chocolate Lane',
  city: 'Tiny Town'
}})

Running labeled tests.

function test(subject, expecations) {
  expectations.forEach(function(expectation)) {
    consol.log('test: ' + subject + expectation.label);
    expectation.test(subject);
  }
}

The plugin integrates nicely with mocha-when-then.

 
shouldHaveAddress = should.have.property('address')
shouldHaveAddress.label = 'should have address'
 
Given 'person', {address: {name: 'Willy'}}
Then 'person', shouldHaveAddress.with.key('name')
 
When -> @person.address.street = 'Chocolate Lane'
And  -> @person.address.city = 'Tiny Town'
Then 'person', shouldHaveAdress.with.key('street')
And  'person', shouldHaveAdress.with.key('city')

This creates the following test lables

person should have address with key name
person should have address with key street
person should have address with key city