Add test to ensure comments don't get duplicated
Add test to ensure comments don't get duplicated

gforcada/isort,AbsoluteMSTR/isort,jmullan/isort,leepa/isort,aequitas/isort,levic/isort,levic/isort,adamchainz/isort,adamchainz/isort,graingert/isort,PyCQA/isort,jmullan/isort,graingert/isort,PyCQA/isort,leepa/isort,AbsoluteMSTR/isort,aequitas/isort,gforcada/isort