Top 20 NuGet Unit Testing Packages

Base class to setup testing SQL interaction without databases using System.Data.Fakes and Moq
Aurochses.Xunit.AspNetCore.Mvc is a library for creating xUnit tests for ASP.NET Core MVC.
Sourcery for SauceLabs - Unlocking SauceLabs capability (Commercial product from fullcirclesolutions.com.au. Only $99.)
Feature flag utilities for .NET - based on etsy and reddit feature flag implementations.
Early preview of some testing helpers for using Moq with Entity Framework.
Utilities for unit testing using xunit framework.
BDD Framework for xUnit and .Net Core
Provides LightBDD integration with Autofac, allowing to use Autofac as DI container for LightBDD scenarios.
A lightweight framework for creating unit tests for Roslyn diagnostic analyzers, code fixes and refactorings using NUnit. This is a NetStandard retarget of Dustin Campbell's library, targetting newer versions of CodeAnalysis packages.
Easy way to tests queries generated by EntityFramework.
Provides some additional xunit abstractions to make integration tests easier.
SpecsFor is another Behavior-Driven Development framework that focuses on ease of use for *developers* by minimizing testing friction.
SecByte.Xunit.Gherkin is a modified version of Xunit.Gherkin.Quick
Framework to help testing Restful APIs in a fluent style that are easy to write and understand. Allows you to write your Api Requests and Asserting the response in a fluent manner. Compatible with NUnit, MSTest, XUnit and any test runner.
Package to help using Newton JsonSchema package to validate response models from an Integration test using RestFluencing.