Needs random tests

Your fixed tests does not consider the case where there will be two consecutive blocks together (e.g 3141 => 1111111).

This is not a valid inversal of look-and-say numbers.

This "modified" kata does not make any sense: The previous sequence is always ambiguious (e.g 112 can mean 11 2s or 2 11s).

Almost a duplicate:
http://www.codewars.com/kata/look-and-say-numbers
http://www.codewars.com/kata/the-look-and-say-sequence
http://www.codewars.com/kata/conways-look-and-say-generalized
http://www.codewars.com/kata/look-and-say-numbers-1