fails:Array#delete_if removes each element for which block returns true
fails:Array#delete_if returns an Enumerator if no block given
fails:Array#delete_if returns an Enumerator if no block given, and the enumerator can modify the original array
fails:Array#delete_if returns an Enumerator if no block given, and the array is frozen
fails:Array#delete_if raises a RuntimeError on a frozen array
fails:Array#delete_if raises a RuntimeError on an empty frozen array
