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