title: Can I set a conditional compilation constant in a web.config or app.config, if so how?
body: <p>I want to do <a href="http://msdn.microsoft.com/en-us/library/4y6tbswk%28v=vs.71%29.aspx" rel="nofollow">this</a> sort of thing.</p>
  
  <p>Can I define my symbol (TESTING or DEBUG etc) in my app.config file?  If so can you provide an example of what the app.config would look like as I'm unsure where to start?</p>
  
  <p><strong>Edit</strong>: Added app.config to the title as I want to do this in an app.config</p>
  
  <p><strong>Update</strong>: It seems that I can only set conditional compilation constants at build time (web.config and app.config are used during runtime and only after the assembly has been compiled).  To set conditional compilation constants I need to do this in the csproj file or options in msbuild.</p>