nunit

NUnit is an open-source unit testing framework for the .NET platform. It is inspired by JUnit and provides a simple, extensible way to write and run tests for .NET applications. The framework emphasizes readability and maintainability, with a rich set of attributes and an assertion library that supports both classic and constraint-based syntax.

NUnit was created to bring the testing concepts of JUnit to the .NET world. It evolved into multiple major versions, with NUnit 3 introducing a new engine and a decoupled architecture that separates the test framework from the test runner, enabling new runners and better compatibility with modern .NET runtimes. NUnit 2.x and 3.x are the most widely used series.

Key features include attributes such as [Test], [TestFixture], [SetUp], [TearDown], [OneTimeSetUp], and [OneTimeTearDown], along with parameterized testing via [TestCase] and [TestCaseSource]. The Assert API supports classic assertions (e.g., Assert.AreEqual) and a constraint-based style (Assert.That(..., Is.EqualTo(...))). NUnit also supports test categories and conditional test execution.

Runners and integration: NUnit provides the Console runner and (historically) a GUI runner, and it integrates with IDEs through test adapters for Visual Studio and other environments. The NUnit 3 architecture uses an Engine plus adapters, enabling broad tooling support and CI integration.

Supported platforms include the .NET Framework, .NET Core, and newer .NET versions, with ongoing development and community involvement in the open-source project. NUnit is widely used in .NET testing to ensure code correctness and maintainability.