I can’t comment on the evolution side of this but, on the practical front…
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If you’re specific concern is testing deprecated code, mark your test method as deprecated. The system will still run it but, because it’s deprecated, it won’t generate deprecation warnings. 
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In other situations I use the protocol workaround described here. 
Needless to say, the second point does not make me happy (r. 31131633)-:
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Quinn “The Eskimo!” @ DTS @ Apple