Fixture dependencies?

[jackfirth]

• Module A defines fixture F
• Module B defines fixture G in terms of F's current value, making G depend on F
• Test T declares that it uses fixture G
• Both fixtures F and G are initialized within test T

The current alternative would be to bundle the disposable underlying F with a function producing the disposable for G using disposable-chain, then providing a "compound fixture" F2+G and convenience function to get the current values of F2 and G out of the compound value. But this means that if a test uses F, and another test inside that test uses G, two instances of F will be created. Furthermore, an extra F will be created for every single fixture built on top of F.

A hidden global parameter in the fixture library that maps gensyms stored in fixtures to current values could be used to implement some sort of automatic fixture dependency system. Or maybe a fixture could wrap a function producing a disposable plus dependency fixtures? Or something.