"Hello World" - The TDD way?

Assuming you know unit testing, and asuming you understand the tdd "red green refactor process" (since you said you are familiar with TDD) Ill quickly explain a typical tdd thought process.

Your TDD life will be made a lot easier if you think of a particular unit of problem and every other connected things should be thought of in terms of dependencies. here is a sample

scenario:- I want my program to display hello world on the console.

tdd thought process:-

"I think my program will start running then call the console program passing my message to it and then I expect my console program to display it on the screen"

"so i need to test that when i run my program, it should call the console program "

"now what are the dependencies? hmm I know that the console program is one of them. I don't need to worry about how the console will get the message to the screen (calling the io device, printing and all that) I just need to know that my program successfully called the console program. I need to trust that the console program works and if it doesn't, then at the moment i am not responsible for testing and making sure it works. the responsibility I want to test is that my program when it starts up calls the console program. "

"but i don't even know exactly what console program to call. well I know of System.console.Writeline (concrete implementation) but then this may change in future due to change in requirements, so what do i do?"

"Well , I will depend on interface (or abstraction) rather than concrete implementation, then i can create a fake console implementing the interface which i can test against"

  public interface Iconsole
    {
       void WriteToConsole(string msg);
    }



 public class FakeConsole : Iconsole
    {
        public bool IsCalled = false;

        public void WriteToConsole(string msg)
        {
            IsCalled = true;
        }
    }

I have

In java you could capture ("redirect") the System.out stream and read its contents. I'm sure the same could be done in C#. It's only a few lines of code in java, so I'm sure it won't be much more in C#