Windmill vs Cucumber-JVM comparison of testing frameworks
What are the differences between Windmill and Cucumber-JVM?

Windmill

https://pypi.org/project/windmill/

Cucumber-JVM

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

Python

Java

Category

UI Testing

Acceptance Testing

General info

Windmill is an Open Source Web UI testing framework for Python

Windmill is an Open Source AJAX Web UI testing framework that implements in-browser recording and playback, cross browser testing and test integration

Cucumber-JVM is a pure Java implementation of Cucumber

The specifications are written in plain texts, which allows them to be easily understandable by all stakeholders.
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

Its main function is testing of front-end components and functionality

Yes

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

No

Yes

You can test back-end components such as API's using rest&soap clients, and databases
Fixtures
Allows defining a fixed, specific states of data (fixtures) that are test-local. This ensures specific environment for a single test

N/A

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
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.

N/A

Yes

You can group your fixtures inside your fixtures directories
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

By using third party libraries

N/A

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)

N/A

Yes

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

N/A

No

Other
Other useful information about the testing framework