A simple package by @ardalis and @nimblepros with guard clause helper methods. See docs for how to extend using your own extension methods defined in your project.
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.
A JavaScript library with function argument assertions, a function parser and assertion wrapper functionality. By wrapping your functions you get defined, notNull, bool, func, number, object, string and notEmpty assertions for free. The interface is specially optimised for the Visual Studio...
More information
Testify is a unit test assertions, test data creation and contract verification framework. It's not dependent on any specific unit testing framework. Testify.Moq adds mocking support via Moq.