SOLUTION: The log file is definitely changing the case of the variables as they appear in .conf 😅.

I appreciate the effort! Further to this, I seems like if I change my function and the expected result to compare lists instead of 'make-ta' they pass!

(check-expect (sub-slot 1 SOBA) (make-ta "Soba" 1 (list 3))) ; subtract one shift <--- FAIL
(check-expect (sub-slot 3 SOBA) (make-ta "Soba" 1 (list 1))) ; subtract a different shift <--- FAIL

(define (sub-slot slot ta)
  (cond [(and (> (ta-max ta) 0) (> (length (ta-avail ta)) 1))
              (make-ta (ta-name ta) 
                       (sub1 (ta-max ta))
                       (remq slot (ta-avail ta)))]
              [else empty]))

(check-expect (sub-slot 1 SOBA) (make-ta "Soba" 1 (list 3))) ; subtract one shift <--- FAIL
(check-expect (sub-slot 3 SOBA) (list "Soba" 1 (list 1))) ; subtract a different shift <--- PASS

(define (sub-slot slot ta)
  (cond [(and (> (ta-max ta) 0) (> (length (ta-avail ta)) 1))
              (list (ta-name ta) 
                       (sub1 (ta-max ta))
                       (remq slot (ta-avail ta)))]
              [else empty]))

This is the final problem of the course 😅. I'm going to try and get to the bottom of this rather than work around with lists (which is what I did last time). I must have some misunderstanding with make- functions...

https://docs.racket-lang.org/... Making the structs transparent seems to be a better work-around for now.

Thanks. I did create a persistent volume, but I thought that deleting the files would trigger them to be recreated when the container restarts.