I kind of screwed something up, but that's life.

I have an extensive program written in Framework. I then wrote a test application that can perform a series of iteration tests on some objects in one DLL. Unfortunately, I wrote the test application in .NET 5. For the most part, this has not caused a problem. However, I just ran into an issue, and I'm pretty sure it has to do with the fact that the program is Framework and the test app is .NET 5. I'm wondering if there is a way around it.

A recent test I added into the test app is testing a function in a class from a DLL. The function makes use of the JavaScriptSerializer class from System.Web.Extensions. The test app can't call the function in the DLL. It can create the class, but when it tries to call that function it crashes with an error saying that System.Web.Extensions doesn't exist. I believe that's true for .NET 5, since all the JSON stuff was replaced. I believe that all the other testing has largely functioned because it doesn't stray into that area, or anything else that changed from Framework to Core.

Is there a way around this other than moving the test app back to Framework?

I've found that working from Framework to Core puts up some interesting problems.