XCTest vs Chai comparison of testing frameworks
What are the differences between XCTest and Chai?

XCTest

https://developer.apple.com/documentation/xctest

Chai

https://www.chaijs.com
Programming language

Swift

JavaScript

Category

Unit Testing, Performance Testing

Unit Testing

General info

XCTest is the default testing framework for unit tests, performance tests, and some level of UI tests for iOS apps.

XCTest framework is a testing framework that enables developers write basic unit tests, performance tests, and some level of UI tests for iOS apps.

Chai is a BDD / TDD assertion library for Node.js and the browser that can be paired with any JavaScript testing framework.

Chai is an assertion library, similar to Node's built-in assert and makes testing easier by giving you many assertions you can run against your code. It also includes a robust Plugin architecture for extending Chai's assertions and interfaces.
xUnit
Set of frameworks originating from SUnit (Smalltalk's testing framework). They share similar structure and functionality.

Yes

Yes, it is an xUnit style framework

N/A

Client-side
Allows testing code execution on the client, such as a web browser

Yes

Developers can test individual front-end components with XCTest

Yes

Chai can be used in a browser environment to test front-end components and functionality
Server-side
Allows testing the bahovior of a server-side code

Yes

Yes, developers can test individual back-end components with XCTest

Yes

Chai is used in a Node.JS environment to test server behaviour and functionality
Fixtures
Allows defining a fixed, specific states of data (fixtures) that are test-local. This ensures specific environment for a single test

Yes

XCTest contains setup() and teardown() fixture methods for setting up and destroying test environments

N/A

Group fixtures
Allows defining a fixed, specific states of data for a group of tests (group-fixtures). This ensures specific environment for a given group of tests.

Yes

Group fixtures are available in XCTest

N/A

Generators
Supports data generators for tests. Data generators generate input data for test. The test is then run for each input data produced in this way.

N/A

Yes

By using chai-spec-generator plugin which will generate chai test specs from a JavaScript object
Licence
Licence type governing the use and redistribution of the software

Apache License 2.0

MIT License

Mocks
Mocks are objects that simulate the behavior of real objects. Using mocks allows testing some part of the code in isolation (with other parts mocked when needed)

Yes

You can create protocol mocks and class mocks with libraries such as MockFive or Cuckoo

Yes

By using by using a third party library like chai-jest-mocks which is a chai plugin that adds assertions for jest mock functions. You can also use sinon.js
Grouping
Allows organizing tests in groups

Yes

Developers can define test suites from the XCTestSuite class

N/A

Other
Other useful information about the testing framework