If you're an end user, not a build tool, you'd rather want to place that in .git/info/exclude inside the repo. It's effectively another gitignore file, which won't be committed.

But if you do need something like this for a build tool, then yeah, you can create a file /test/.gitignore with these contents:

real-person-first-last.json
.gitignore

Then running git add . just adds /test/fake-person-first-last.json.

Both /test/.gitignore and /test/real-person-first-last.json would be ignored right away.