unit testing version statements

[Robert burner Schadek via Digitalmars-d-learn]

How do I unit test version statements without fixing version in 
place forever.

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bool fun() {
     version(Version1) return true;
     else version(Version2) return true;
     else return false;
}

version = Version1;
unittest {
     assert(fun());
}

version = Version2;
unittest {
     assert(fun());
}

unittest {
     assert(!fun());
}

version = None; // is there anyway to save and reset the version
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