C# – How to Console.WriteLine from [TestMethod]

I am not sure I understand why do you want to do this (apart from dealing with an intellectual challenge). This kind of code, where you work directly with some system level API, is very hard to unit test, TDD style or not, and to be frank, I don't find it very valuable to try it in a real project.

Most of the task you describe is calling the right low level API method with the right parameter. And the rest of the code as is may be so trivial, it wouldn't necessarily warrant the introduction of a dedicated interface, mock objects etc. I would be content having an integration test to verify on a higher level that the whole stuff works. But this is just my 2 cents.

Unit testing for me is not about following rulebooks or strict definitions. In real life, I don't really care whether my tests are "real" unit tests or not; as long as my code is being covered by automated and repeatable tests, I am fine. I prefer the pragmatic approach.

I mentioned in one of my comments to simoraman's answer that I had thought of a couple of ways to do this. One of my options was similar to the suggestion in Jalayn's answer to created a duplicate project and generate a DLL, while my other idea was to simply link to the files in the project where there was code I wanted to test. While both options could be made to work, they are less than ideal.

In the second case, I'd have a mess of unit dependencies to manage unless I could really tease apart the architecture to minimize dependencies. This is fine for smaller projects, but larger ones could easily become a real mess to manage. My biggest resistance to this option however is the sheer inelegance of it. Sure I could get it to work, but in doing so I effectively need to break encapsulation to test the internals of an assembly directly via source, rather than testing the via the public interfaces, which in my mind is a big no-no. Likewise having an additional project file would mean either duplicating efforts in two projects at a time, or finding a way to add project file settings automatically to two files at a time, or remembering to copy and rename the project field each time I build. This can be automated on the build server perhaps, but would be a pain to manage in the IDE. Again, it can work, but it's a kludge at best, and a nuisance at worse if you get it wrong.

The best way seems to be to do as whatsisname commented to my question, and to simply include the EXE as a reference in the test project. It turns out that an EXE is effectively treated the same way as a DLL in this case, and I am able to access all of my nicely layered classes to test whatever floats my boat.