Top 20 NuGet assertion Packages
A simple package with guard clause helper methods. See docs for how to extend using your own extension methods.
CodeJam is a set of handy reusable .NET components that can simplify your daily work and save your time when you copy and paste your favorite helper methods and classes from one project to another.
Generalized assertion library, covering argument, operation, and unit test assertions.
Testify is a unit test assertions, test data creation and contract verification framework. It's not dependent on any specific unit testing framework.
A collection of xUnit.net assertions, tailored for Tiger libraries. (As source.)
Extensions for VisualStudio UnitTest's Assert class to simplify e.g. testing of view models.
Use code snippet 'assertion' to get the declaration at the top of the file. Then just use Assert.Equal(...) and the like.