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

NUnit

https://nunit.org/

Cucumber

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

.NET

Ruby

Category

Unit Testing

Acceptance Testing

General info

NUnit is an open-source unit testing framework for Microsoft .NET.

NUnit was Initially ported from JUnit. Tests can be run from a console runner, within Visual Studio through a Test Adapter or through 3rd party runners. Tests can be run in parallel and has Strong support for data driven tests. Unit supports multiple platforms including .NET Core, Xamarin Mobile, Compact Framework and Silverlight.

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.

Yes

Nunit is one of many programs in the xUnit family

No

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

Yes

You can test front-end components with NUnit since it is a Unit testing framework the application is isolated into diverse modules which are tested independently

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 components with NUnit, it is a Unit testing framework hence the application is isolated into diverse modules which are tested independently

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

NUnit contains the fixture methods SetUp to initialize your test environment and TearDown method to destroy a test environment

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

Group fixtures are available in NUnit

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

MIT 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 create mock objects using the third party library moq

Yes

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

Yes

You can group tests into suites with NUnit

No

Other
Other useful information about the testing framework