You can contribute to Hectoparsec!
Hectoparsec uses Cabal for building and Haskell Language Server for IDE integration.
Hectoparsec currently uses hspec as the test framework. You can run tests with cabal test.
If you would like to rerun failed tests, follow the instructions here.
If you would like to run a specific test, use cabal run hectoparsec-test -- -m PATTERN, where the pattern syntax is as specified in here.