¶ Chai
¶ SDK Libraries
There is a moment in every developer’s journey when code begins to feel less like a set of instructions and more like a language with its own rhythm, its own emotional weight, and its own philosophy. The deeper you go, the more you realize that the tools you choose shape not just the way you build software but also the way you think about building it. Some tools feel mechanical and distant. Others feel like an extension of your mind. And then there are tools like Chai, which quietly empower you with an elegance that’s easy to overlook until you spend time with it.
Chai is one of those libraries that’s deceptively simple on the surface. To the uninitiated, it may look like just another assertion library—a line or two of syntactic sugar that helps you test code more comfortably. But anyone who has spent real time with it knows it is far more than a helper. It’s a companion to better thinking, better structuring, and ultimately better craftsmanship. At the heart of Chai is a philosophy that values clarity, honesty, and natural expression. It encourages you to write tests in a way that feels like describing your intentions rather than decoding them. And when you use it long enough, something subtle happens: your approach to testing, validation, and even architectural design begins to shift.
This course—one hundred articles spanning from foundational principles to deep, real-world mastery—is not just an exploration of a library. It’s an exploration of a mindset. Chai represents an attitude toward development where readability isn’t a luxury, but a baseline expectation; where correctness and clarity walk side by side; where the tools you use don’t get in the way of the thoughts you’re trying to express. With so many SDKs and libraries crowding the modern development landscape, it’s refreshing to find one that still holds to the idea that code should feel alive, meaningful, and expressive.
Before we venture deeper, it’s worth pausing on why an entire course should begin with something as unassuming as Chai. There are flashier libraries out there—frameworks bursting with features, systems that promise to automate away all complexity, environments that tout themselves as complete ecosystems. Yet complexity isn’t always where mastery begins. Often, mastery begins with tools that quietly shape the foundation: the tools that teach the developer how to reason, how to test assumptions, how to articulate intent with precision. Testing has always been one of the most reliable mirrors of a developer’s thought process. And an assertion library like Chai reflects not only the correctness of code but the clarity of the person behind it.
In a world where so much software is rushed—deployed before it’s ready, patched on the fly, updated with a sense of perpetual urgency—Chai brings back the practice of slowing down, not to be inefficient, but to be intentional. When you write a sentence like “expect(result).to.equal(42)”, you aren’t just verifying output. You’re documenting a story. You’re telling the future reader, whoever they may be (including yourself), exactly what you believed the system should do at that moment in time. And unlike many technical statements, this one is understandable even to someone outside the code. That’s the magic of Chai: it narrows the gap between the technical and the human.
This course is built with that spirit in mind. As we progress, you’ll see that understanding Chai isn’t just about memorizing assertions or knowing when to use should, expect, or assert. It’s about learning how to express your ideas more clearly. It’s about developing a testing style that feels intuitive and honest, one that supports your growth rather than constrains it. By the time you finish all one hundred articles, you won’t just know Chai. You’ll know how to bring a deeper sense of clarity and purpose into the way you work with SDKs and libraries in general.
Developers often underestimate the emotional side of coding. We talk about performance, scalability, compatibility, and all the technical metrics you’d expect. But few people talk about how a library feels. Tools that feel rigid or awkward often create friction in a project, even if they’re objectively powerful. A library like Chai, though, feels inviting. It’s not trying to impress you with cleverness or overwhelm you with options. Instead, it offers a small but beautiful set of expressive tools and then steps out of the way, letting you shape your tests like a craftsman shapes a piece of wood—carefully, intentionally, with attention to every curve and edge. You’ll find that once you embrace its style, your testing becomes less of a chore and more of a creative process.
Of course, part of what makes Chai so beloved is its flexibility. Some developers want their tests to read like English sentences. Others prefer the classic assertion style they grew up with. Chai supports both with ease, allowing each person to work the way that suits them best. This adaptability is one of the reasons it fits so naturally into the wider ecosystem of SDKs and libraries. Whether you’re working with Node.js, building a browser-based project, or integrating with a complex testing framework, Chai adapts without demanding special treatment. It’s the sort of tool you can bring into almost any context without creating friction.
But beyond all the praise—and there will be plenty throughout this course—it’s also important to acknowledge that learning Chai deeply means learning the broader world it lives in. Assertions are the last step; understanding what you’re asserting, why you’re asserting it, and how those checks fit into your larger development workflow is where the real growth happens. Throughout these hundred articles, we’ll explore not just the “how” of Chai but also the “why.” We’ll dig into patterns that make tests resilient rather than brittle. We’ll examine how to structure test suites so they communicate clearly with future contributors. We’ll explore how Chai integrates with modern test runners, how it supports asynchronous logic, and how its expressive syntax can help you design more maintainable architectures.
Testing can sometimes feel like a second thought in software development. Many developers, especially beginners, see it as something they should do rather than something they want to do. That reluctance comes from a misunderstanding of testing’s purpose. Testing isn’t about proving your intelligence or catching every bug. It’s about gaining confidence, reducing anxiety, and building a safety net that lets you move faster without fear. When done well, tests make development more playful, more experimental. Chai encourages that kind of environment because it’s pleasant to use. The less friction you feel when writing a test, the more often you’ll write them, and the better your codebase becomes.
As you move forward, think of this introduction as your welcome into a different mode of working. A mode where your tools don’t fight you. A mode where clarity matters, where syntax supports your thinking, and where a simple assertion can become a moment of insight. The journey through this course will give you not only the technical skills to wield Chai with confidence but also the mindset to approach libraries and SDKs with more intuition and artistry.
Every great craftsperson begins with simple, honest tools. Chai might seem like a modest place to start a long journey, but its influence stretches far beyond its lines of code. It teaches you precision. It teaches you readability. It teaches you that small tools, when designed with care, can have an outsized impact on the quality of your work. Over the next hundred articles, we’ll honor that spirit and build on it—expanding your understanding, deepening your intuition, and helping you forge a testing practice that grows naturally with your skills.
For now, let this serve as your first step. Take a deep breath, clear your mind, and let the gentle simplicity of Chai invite you into a richer, clearer, more expressive way of writing tests—and, by extension, writing software. The journey ahead is long, but it’s one worth taking.
¶ Chai
¶ Beginner Level (Foundational Concepts)
1. Introduction to Chai
2. Installing and Setting Up Chai
3. Overview of Chai Assertion Styles
4. Understanding Assert Style
5. Understanding Expect Style
6. Understanding Should Style
7. Writing Your First Test with Chai
8. Basic Assertions with Assert Style
9. Basic Assertions with Expect Style
10. Basic Assertions with Should Style
11. Comparing Values: Equal, Eql, and Deep Equal
12. Checking Truthiness: True, False, and Ok
13. Checking Falsiness: Not True, Not False, and Not Ok
14. Checking for Null and Undefined
15. Checking for NaN
16. Checking for Type: A, An, and Instanceof
17. Checking for Length: LengthOf
18. Checking for Inclusion: Include and Contain
19. Checking for Exclusion: Not Include and Not Contain
20. Checking for Property: Property and OwnProperty
21. Checking for Method: RespondTo
22. Checking for Equality: Equal and Eql
23. Checking for Inequality: Not Equal and Not Eql
24. Checking for Greater Than and Less Than
25. Checking for Range: Within and Above
26. Checking for Match: Match and String
27. Checking for Empty: Empty
28. Checking for Keys: Keys
29. Checking for Throw: Throw
30. Writing Basic Test Suites with Mocha and Chai
¶ Intermediate Level (Core Concepts and Advanced Assertions)
31. Advanced Assertions with Assert Style
32. Advanced Assertions with Expect Style
33. Advanced Assertions with Should Style
34. Chaining Assertions
35. Negating Assertions
36. Custom Error Messages
37. Asynchronous Testing with Chai
38. Testing Promises with Chai
39. Testing Callbacks with Chai
40. Testing Async/Await with Chai
41. Using Chai with Mocha
42. Using Chai with Jest
43. Using Chai with Karma
44. Using Chai with Cypress
45. Using Chai with Protractor
46. Using Chai with Nightwatch
47. Using Chai with WebdriverIO
48. Using Chai with Puppeteer
49. Using Chai with Playwright
50. Using Chai with Ava
51. Using Chai with Jasmine
52. Using Chai with Tape
53. Using Chai with QUnit
54. Using Chai with TestCafe
55. Using Chai with Intern
56. Using Chai with Lab
57. Using Chai with Uvu
58. Using Chai with Zora
59. Using Chai with Node-Tap
60. Using Chai with Vitest
¶ Advanced Level (High-Level Concepts and Applications)
61. Custom Assertions with Chai
62. Plugins for Chai
63. Using Chai-HTTP for API Testing
64. Using Chai-JSON-Schema for JSON Validation
65. Using Chai-Datetime for Date and Time Assertions
66. Using Chai-Files for File Assertions
67. Using Chai-Arrays for Array Assertions
68. Using Chai-As-Promised for Promise Assertions
69. Using Chai-Sinon for Spy, Stub, and Mock Assertions
70. Using Chai-Immutable for Immutable.js Assertions
71. Using Chai-Enzyme for React Component Testing
72. Using Chai-JQuery for jQuery Assertions
73. Using Chai-Webdriver for Webdriver Assertions
74. Using Chai-Express-Handler for Express Middleware Testing
75. Using Chai-GraphQL for GraphQL Assertions
76. Using Chai-Fuzzy for Fuzzy Assertions
77. Using Chai-Deep-Match for Deep Matching Assertions
78. Using Chai-Change for Change Assertions
79. Using Chai-Subset for Subset Assertions
80. Using Chai-Exclude for Exclusion Assertions
81. Using Chai-Interface for Interface Assertions
82. Using Chai-Iterator for Iterator Assertions
83. Using Chai-Things for Collection Assertions
84. Using Chai-String for String Assertions
85. Using Chai-Fs for Filesystem Assertions
86. Using Chai-Url for URL Assertions
87. Using Chai-Oauth2 for OAuth2 Assertions
88. Using Chai-Redis for Redis Assertions
89. Using Chai-Mongo for MongoDB Assertions
90. Using Chai-Passport for Passport Assertions
91. Using Chai-Socket for Socket.IO Assertions
92. Using Chai-Websocket for WebSocket Assertions
93. Using Chai-Amqp for AMQP Assertions
94. Using Chai-Kafka for Kafka Assertions
95. Using Chai-Rabbitmq for RabbitMQ Assertions
96. Using Chai-Nats for NATS Assertions
97. Using Chai-Grpc for gRPC Assertions
98. Using Chai-Thrift for Thrift Assertions
99. Using Chai-Xml for XML Assertions
100. Real-World Case Studies with Chai