fails:Hash#reject! raises a TypeError if called on a frozen instance
fails:Hash#reject returns an Enumerator if called on a non-empty hash without a block
fails:Hash#reject returns an Enumerator if called on an empty hash without a block
fails:Hash#reject! returns an Enumerator when called on a non-empty hash without a block
fails:Hash#reject! returns an Enumerator when called on an empty hash without a block
