[review v3] testsuite, cp: increase the coverage of testing pass-by-ref arguments

[Aktemur, Tankut Baris]

> > The version with Luis' comment addressed is below.
> 
> Thanks, that looks good to me.
> 
> Simon

Thank you.  Pushed with commit hash 5f440116e87.

(Sorry about the previous email.  It went out by mistake before it was complete.)

-Baris

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