chai

What is chai?

Chai is a BDD / TDD assertion library for node and the browser that can be delightfully paired with any javascript testing framework. It provides functions to express assertions in a readable language, supporting both 'should' and 'expect' style syntaxes, as well as a traditional 'assert' style interface.

What are chai's main functionalities?

Should Style Assertions

Allows you to write assertions in a more human-readable form, which reads like English. The 'should' style extends each object with a 'should' property to start your chain.

chai.should();
var should = chai.should();
should.exist(value, 'value should not be null or undefined');

Expect Style Assertions

Provides a function called 'expect' to make assertions about values. This style is similar to 'should' but does not extend any objects, which is useful for working with libraries that don't allow object extensions.

var expect = chai.expect;
expect(value).to.exist.and.be.an('object');

Assert Style Assertions

Offers a more traditional testing interface, which is similar to Node.js' core 'assert' module but with more capabilities and better error messages.

var assert = chai.assert;
assert.typeOf(value, 'string', 'value is a string');

Chainable Language Chains

Provides chainable getters to improve the readability of your assertions, allowing you to write more expressive tests.

expect(value).to.be.an('array').that.includes(3);

Plugins

Supports plugins to extend its core functionalities, which can be used to add new assertions, matchers, or methods to the library.

var chaiHttp = require('chai-http');
chai.use(chaiHttp);

Other packages similar to chai

jest

Jest is a delightful JavaScript Testing Framework with a focus on simplicity. It works out of the box for any React project and includes its own assertion library, which provides a similar but more integrated testing experience compared to Chai.

jasmine

Jasmine is a behavior-driven development framework for testing JavaScript code. It does not rely on browsers, DOM, or any JavaScript framework, making it suitable for websites, Node.js projects, or anywhere JavaScript can run. It has its own assertion syntax that is somewhat similar to Chai's 'expect' syntax.

expect.js

Expect.js is a minimalistic BDD-style assertions library that can be considered an alternative to Chai's 'expect' interface. It provides a similar API but is no longer actively maintained.

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