fails:Hash#compare_by_identity causes future comparisons on the receiver to be made by identity
fails:Hash#compare_by_identity causes #compare_by_identity? to return true
fails:Hash#compare_by_identity returns self
fails:Hash#compare_by_identity uses the semantics of BasicObject#equal? to determine key identity
fails:Hash#compare_by_identity uses #equal? semantics, but doesn't actually call #equal? to determine identity
fails:Hash#compare_by_identity regards #dup'd objects as having different identities
fails:Hash#compare_by_identity regards #clone'd objects as having different identities
fails:Hash#compare_by_identity regards references to the same object as having the same identity
fails:Hash#compare_by_identity raises a RuntimeError on frozen hashes
fails:Hash#compare_by_identity perists over #dups
fails:Hash#compare_by_identity persists over #clones
fails:Hash#compare_by_identity does not copy string keys
fails:Hash#compare_by_identity? returns false by default
fails:Hash#compare_by_identity? returns true once #compare_by_identity has been invoked on self
fails:Hash#compare_by_identity? returns true when called multiple times on the same ident hash
