Housekeeping

Did not like how we held the `err.txt` example in a generated test folder whilst also holding onto the irrelevant `gjf` and `sub` file. Here it is moved to a better spot (could be changed again in the future...) and this way when we run the test, it copies the error file to the designated folder for testing and then afterwards we can aggressively remove the generated test folder.

Author: calvinp0