Visual Studio during debug execute few lines of test code in immediate window

 You can run a lot of things in the Immediate window (Debug >> Windows >> Immediate)

For example, you can run the following: System.IO.File.WriteAllText(@"c:\temp\blah.txt", "Hi there!");

https://stackoverflow.com/questions/384743/how-to-quickly-code-and-run-small-c-sharp-code