fails:Array#index returns the index of the first element == to object
fails:Array#index returns 0 if first element == to object
fails:Array#index returns size-1 if only last element == to object
fails:Array#index returns nil if no element == to object
fails:Array#index accepts a block instead of an argument
fails:Array#index ignores the block if there is an argument
fails:Array#index given no argument and no block produces an Enumerator
