Mocking & Test Doubles

Mockito

mockito/mockito

Popular

The most popular mocking framework for Java unit tests, with a clean verify/when API.

WireMock

wiremock/wiremock

Popular

HTTP API simulator for stubbing and recording external services, run in-JVM, standalone or in Docker.

Sinon.JS

sinonjs/sinon

Standalone spies, stubs, mocks and fake timers for any JavaScript test framework.

nock

nock/nock

HTTP server mocking and expectations for Node.js by intercepting outgoing requests.

MockK

mockk/mockk

Mocking library built for Kotlin, supporting coroutines, objects, extension functions and final classes.

MSW

mswjs/msw

Popular

Mock Service Worker: intercepts network requests to mock APIs in tests, Storybook and the browser.

NSubstitute

nsubstitute/NSubstitute

Friendly .NET mocking library with a concise syntax; a popular alternative to Moq.

Moq

devlooped/moq

Long-standing LINQ-based mocking library for .NET, still one of the most downloaded on NuGet.

Mockoon

mockoon/mockoon

Desktop app and CLI for spinning up local mock REST APIs in seconds, importable from OpenAPI.

JSON Server

typicode/json-server

Full fake REST API from a JSON file in seconds, handy for prototyping and frontend tests.