This is kinda hard to follow.  (And I'm not even sure if `fail` is available in the example group context...but of course the point here is that it doesn't get to that line).  Instead, what do you think about doing this?

* Put this context in a separate file.
* Have two `When...Then` sections for this scenario:
  * The first will run the file containing the two contexts that define and use an example groups 
  * The second will run the file containing the context that (wrongly) uses the context even though one isn't available.  It can verify that it fails with an appropriate error.