1) Strings are mutable in ruby, so get rid of all those +'s.

2) Don't use back slashes in strings--unless you specifically intend to 
use an escape character.

3)
> My final dilemma is how to get the value of STUB_CALLS into
> Templates.rb by defining it in my test program Impl.rb.

Why can't your methods have a 'debug' parameter with a default value? 
Then for debugging, you can 'override' the default.

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