Web.Config transformations

We have the following in our web.config:

  <appSettings configSource="config\app.debug.config" />  <connectionStrings configSource="config\connectionstring.debug.config" />

How can we use transformation in a TEST build profile to make the elements this:

  <appSettings configSource="config\app.test.config" />  <connectionStrings configSource="config\connectionstring.test.config" />

Thanks!