Cucumber vs Kiwi comparison of testing frameworks
What are the differences between Cucumber and Kiwi?

Cucumber

https://github.com/cucumber/cucumber-ruby

Kiwi

https://github.com/kiwi-bdd/Kiwi
Programming language

Ruby

Swift

Category

Acceptance Testing

Unit Testing

General info

An automation tool for Behavior-Driven Development

The specifications are written in plain texts, which allows them to be easily understandable for all stakeholders. Cucumber Framework also supports languages beyond Ruby e.g. Java, JavaScript and Scala.

Kiwi is a Behavior Driven Development library for iOS development

The goal behind Kiwi is to provide a BDD library that is simple to setup and use, and create tests that are more readable than what is possible with the bundled test framework.
xUnit
Set of frameworks originating from SUnit (Smalltalk's testing framework). They share similar structure and functionality.

No

Yes

Kiwi is an xUnit style framework
Client-side
Allows testing code execution on the client, such as a web browser

Yes

You can test the front-end part like the GUI using cucumber and selenium, they integrate well to test your front-end.

Yes

You can test front-end components with kiwi
Server-side
Allows testing the bahovior of a server-side code

Yes

You can test back-end components such as APIs using rest & soap clients, and databases using whatever client libraries were provided by the libraries that existed in those stacks

Yes

You can test back-end components with kiwi
Fixtures
Allows defining a fixed, specific states of data (fixtures) that are test-local. This ensures specific environment for a single test

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

Using the cucumber extension aruba you can create fixures in two steps: 1.Create a fixtures-directory; 2.Create fixture files in this directory

Yes

kiwi has a beforeEach(aBlock) which is run before every 'it' block in all enclosed contexts. Code that sets up the particular context should go here and afterEach(aBlock) which is run after every it block in all enclosed contexts
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.

Yes

You can group your fixtures inside your fixtures directories

Yes

through the beforeAll(aBlock) and afterAll(aBlock) functions.
Licence
Licence type governing the use and redistribution of the software

MIT License

Proprietary, Open source

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

By using all of RSpec’s supported mocking frameworks (RSpec, Mocha, RR, Flexmock)

Yes

Kiwi has inbuilt support for stubs and mocks,including null mocks, class mocks, protocol mocks
Grouping
Allows organizing tests in groups

No

Yes

Kiwi uses the block syntax in iOS to define groups of assertions and share setup state between collections of tests
Other
Other useful information about the testing framework