This approach nests the the list. Its good that you get a list of all the start codons, but you have to make sure that the next index you choose is outside the the first chosen ORF. 

Test 3 FAILED: 
Input DNA: GATGTTTATGGGCTAGTAG
Expected Output: ['ATGTTTATGGGC']
Actual (your) Output: ['ATGTTTATGGGC', 'ATGGGC']
FAILED - find all ORFs all frames