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

Cucumber

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

Spock

http://spockframework.org/
Programming language

Ruby

Java

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.

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
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

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

Yes

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

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

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

N/A

Licence
Licence type governing the use and redistribution of the software

MIT License

Apache License 2.0

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

Spock has inbuilt mocking capabilities and has no need for external libraries
Grouping
Allows organizing tests in groups

No

Yes

You can create suites manually in spock
Other
Other useful information about the testing framework