How to quickly debug my code in isolation - internal, developer only, throw-away test

I'm looking for ways to quickly debug the code I've just written to see if it behaves correctly and all my assumptions are correct. I don't want to run the full system yet because parts of infrastructure to get to this code are missing. I use unit testing for it but I find it cumbersome. Is there anything better?

Objectives are:

• Debug any code quickly without creating additional projects, applications etc.
• Easily repeat debugging.
• The test is for this specific purpose, might use fixed file paths, database connections, anything. Typically thrown away after getting things right.
• Need to access internal members of my objects.
• Accessing private member would be great benefit.
• I'm fine with writing test functions directly in my object. Actually this would be preferred.

The dream way of doing it would be:

namespace Aaa
{
    class SomeClass
    {
        public string Name { get; private set; }

        public SomeClass(string name, int value)
        {
            this.Name = name;
            InitializeSth();
        }

        public DoSomethingPublic()
        {
            // ...
        }

        private DoSomethingPrivate()
        {
            // ...
        }

        public static void TestThis()   // <-- debug this
        {
            var obj = new SomeClass();  // <-- put breakpoint here
            obj.DoSomethingPublic();
            obj.DoSomethingPrivate();
        }
    }
}

This is possible in Java and is such a great thing. This allows for accessing private things too.

But I'm open to other options as well. Is there anything like this in VS2015?

What I have tried so far:

• Immediate Window - I don't think it can be configured for such purpose
• C# Interactive - this doesn't seem to support debugging. Or does it?
• Unit testing - this is what I use now (with MSTest). But I find it very cumbersome, because:
  • I need to create new projects, or include references to MS testing assemblies
  • I need to make extra steps to access internal types and members, or change things to public (I don't like this).
  • Even more steps to access private members.
  • I mess with other tests if Unit Testing is used in the project.
  • Starting debugging again needs many clicks instead of sth+sth+F5.
  • There are some workarounds for some of these items, but in general the testing infrastructure seems to be made for a different things and I always have a feeling I'm fighting with it.

I also found some information about Resharper having ability to debug any static function. But I don't want to use Resharper, mainly because of performance.