I was scratching my head because some hooks were passing even though they should clearly have failed.

When running run --all-files with the --verbose flag, I noticed why this was happening:

[do_not_commit] Block if "DO NOT COMMIT" is found..................................................................Passed
hookid: do_not_commit

Executable `ggrep` not found

It seems like the correct behaviour would be to fail and warn user to install ggrep?

For the record, I installed ggrep as follow: brew install homebrew/dupes/grep, and the hooks now fail as expected.