fails:Enumerable#minmax min should return the minimum element
fails:Enumerable#minmax returns [nil, nil] for an empty Enumerable
fails:Enumerable#minmax raises an ArgumentError when elements are incomparable
fails:Enumerable#minmax raises a NoMethodError for elements without #<=>
fails:Enumerable#minmax returns the minimum when using a block rule
fails:Enumerable#minmax gathers whole arrays as elements when each yields multiple
