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

Spek

https://www.spekframework.org/

Cucumber

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

Kotlin

Ruby

Category

Acceptance Testing, Unit Testing

Acceptance Testing

General info

Spek is a specification framework for Kotlin

Spek is a Kotlin-based Specification Testing framework for the JVM. It works as a JUnit 5 Test Engine meaning that we can easily plug it into any project that already uses JUnit 5 to run alongside any other tests that we might have.

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.
xUnit
Set of frameworks originating from SUnit (Smalltalk's testing framework). They share similar structure and functionality.

No

No

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

Yes

Yes you can test front-end behaviour by writing specifications to test front-end functionality. Developers can also write unit tests for individual front-end components.

Yes

You can test the front-end part like the GUI using cucumber and selenium, they integrate well to test your front-end.
Server-side
Allows testing the bahovior of a server-side code

Yes

You can test back-end behaviour and componets by writing specifications to test back-end functionality and unit tests for individual back-end components

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
Fixtures
Allows defining a fixed, specific states of data (fixtures) that are test-local. This ensures specific environment for a single test

Yes

Fixtures are available in spek through functions suchas beforeEachTest() and afterEachTest()

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

spek has group fixtures available through the beforeGroup() and afterGroup() functions

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
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

You can group your fixtures inside your fixtures directories
Licence
Licence type governing the use and redistribution of the software

Modified BSD License

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 use the third party library mockito-kotlin

Yes

By using all of RSpec’s supported mocking frameworks (RSpec, Mocha, RR, Flexmock)
Grouping
Allows organizing tests in groups

Yes

Tests are written using nested lambdas, each scope (level) can either be a group or a test

Yes

Cucumber allows the use of tag Cucumber feature files or individual tests to group tests. Then, you can pass a Cucumber tagged expression at test execution that specifies the tag (grouped) tests to run. https://www.toolsqa.com/cucumber/cucumber-tags/
Other
Other useful information about the testing framework