Running tests locally generates (or changes?) outputs that are not `.gitignore`d

After running tests locally, with `git status` I see...
```shell
...
Untracked files:
  (use "git add <file>..." to include in what will be committed)
	tests/Data/pipeline_output/
	tests/Data/pipeline_output3/

no changes added to commit (use "git add" and/or "git commit -a")
```