How to find path of active app.config file?

I'm trying to finish this exception handler:

if (ConfigurationManager.ConnectionStrings["ConnectionString"]==null)
{
    string pathOfActiveConfigFile = ...?
    throw new ConfigurationErrorsException(
       "You either forgot to set the connection string, or " +
       "you're using a unit test framework that looks for  "+
       "the config file in strage places, update this file : " 
       + pathOfActiveConfigFile);
}

This problem seems to only happen to me when I'm using nUnit.

From stackoverflow

• If you mean you are only getting a null return when you use NUnit, then you probably need to copy the ConnectionString value the your app.config of your application to the app.config of your test library.

  When it is run by the test loader, the test assembly is loaded at runtime and will look in its own app.config (renamed to testAssembly.dll.config at compile time) rather then your applications config file.

  To get the location of the assembly you're running, try

  System.Reflection.Assembly.GetExecutingAssembly().Location
  

• Depending on the location of your config file System.Reflection.Assembly.GetExecutingAssembly().Location might do what you need.

  William Edmondson : Additionally, you can have several "active" config files at the same time. Machine.config, framework level web.config, app level config, etc... so I don't think there is a way to automatically locate a unique connection string file location without parsing through all the possible config files available to your app.

• Try this

  AppDomain.CurrentDomain.SetupInformation.ConfigurationFile
  

  Hope it helps

  John Sibly : Did the job for me - thanks! :o)

• Make sure you click the properties on the file and set it to "copy always" or it will not be in the Debug\ folder with your happy lil dll's to configure where it needs to be and add more cowbell

• Strictly speaking, there is no single configuration file (for non-ASP.NET). There can be three with the inbuilt (System.Configuration) support (in addition to the machine config).

  To get the "global" configuration (exe.config):

  ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None)
                      .FilePath
  

  Use different ConfigurationUserLevel values for per-use roaming and non-roaming configuration files.

  Noam Gal : I first upped the "Answer", which was very helpful. But at the end I really needed this approach, so thanks for putting it up here as well.

• The first time I realized that the Unit testing project referenced the app.config in that project rather then the app.config associated with my production code project (off course, DOH) I just added a line in the Post Build Event of the Prod project that will copy the app.config to the bin folder of the test project.

  Problem solved

  I haven't noticed any weird side effects so far, but I am not sure that this is the right solution, but at least it seems to work.