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

Spock

http://spockframework.org/

Chai

https://www.chaijs.com
Programming language

Java

JavaScript

Category

Unit Testing

Unit Testing

General info

Spock is a testing and specification framework for Java and Groovy applications

Spock has a highly expressive specification language, and due to its JUnit runner, Spock is compatible with most IDEs, build tools, and continuous integration servers.Spock is inspired from JUnit, RSpec, jMock, Mockito, Groovy, Scala, Vulcans among others

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.

No

N/A

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

Yes

Spock tests front-end components and functionality by unit testing individual classes and functions

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

Spock tests back-end components and functionality by unit testing individual classes and functions

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

Spock contains four methods for setting up environments :setup() (run before every feature method), cleanup() (run after every feature method), setupSpec() (run before the first feature method), cleanupSpec() (run after the last feature method)

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

You can use the fixture methods to setup environments for groups of tests.

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

Spock has inbuilt mocking capabilities and has no need for external libraries

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

You can create suites manually in spock

N/A

Other
Other useful information about the testing framework