Tests failing due to some rogue "in" -> "out" regex replacement

One of the odder error messages I've seen in a while, while running npm run test:

$ node -r @std/esm ../../scripts/validate-es5-dependencies.js
Done in 15.63s.
{ Error: Command failed: yarn run test
error Could not open cafile: EISDIR: illegal operation on a directory, read
fs.js:652
  return binding.open(pathModule._makeLong(path), stringToFlags(flags), mode);
                 ^

Error: ENOENT: no such file or directory, open '/Users/stevebennett/odev/freelancoutg/geo/turf/packages/turf-nearest-neighbor-analysis/test/in/brazil-states-bbox.json'

Why is this so weird? Because the actual name of my directory on disk is ".../odev/freelancing/...". Something has replaced the "in" with "out".