This web site on automated testing lists quite a few academic and commercial test case generators. Unfortunately, I don't see any that generate test cases en masse. Most, if not all, seem to generate tests for either one class or one method at a time.
Update: Agitar's claims its JUnit Generator can generate many unit tests quickly. I don't know if it is ...
If you already have the code base written, most likely it won't be testable, you'll have to refactor and that may cause porblems\errors so I recommend using other tools to test your code and validate its stability.
I use Typemock’s ‘Suggest’ tool, it scans your code and generates tests for you, after they are generated you can either save them manually or ...
NCrunch is the tool of my choice.
It's a commercial tool at a price of $159 for a named user license (at the time of writing, of course).
it works on Windows 10
it integrates into Visual Studio 2008 and higher (i.e. is a plugin)
it supports MSTest, NUnit and others
it supports C#, VB.NET and F#
Even some optional features are fulfilled:
it uses a test ...