Here is collection of legacy joystick testers for C64 - Mini.

• Joystick tester raw by enthusi
• NCL Joystick Tester by nucleus/TempesT
• Joystick Tester V1.0 (“Tools11”) by The Digital Underground (TDU)
• Joystick Tester by Danish Science

• Joystick-Testers.d64.zip includes all of above (except 'fancy' one by Danish Science, but includes BASIC programs below)
• storage of all above

Program listings of BASIC testers that could be entered at your C64 - Mini.
You can copy & paste it into e.g. VICE emulator, but some versions needs type case to be changed to lower case. REM statements (or whole program lines including only REMarks) do not need to be typed in / copied.

Quick joystick test:
10 PRINT PEEK(56320),PEEK(56321):GOTO 10

“Joystick tester raw” by enthusi:
(Visual version: changes colors of border. Needs RUN/STOP+RESTORE to stop. Original program separated in two program-lines, to be more easily entered)
1 FORB=0TO17:READA:POKE163+B,A:NEXT:SYS163
2 DATA120,173,0,220,141,32,208,74,74,74,74,41,1,141,33,208,16,239

“Joystick Tester” from “Programmer's Reference Guide” (page 344):
1 REM
2 REM JOYSTICK TESTER PROGRAM FROM
3 REM PROGRAMER'S REF. GUIDE, PAGE 344
4 REM
10 FORK=0TO10:REM SET DIRECTION STRING
20 READDR$(K):NEXT
30 DATA“”,“N”,“S”,“”,“W”,“NW”
40 DATA“SW”,“”,“E”,“NE”,“SE”
50 PRINT“GOING…”;
60 GOSUB100:REM READ THE JOYSTICK
65 IFDR$(JV)=““THEN80:REM CHK IF DIR CHOSEN
70 PRINTDR$(JV);” ”;:REM OUTPUT WHICH DIRECTION
80 IFFR=16THEN60:REM CHECK IF FIRE BUTTON WAS PUSHED
90 PRINT“—F—I—R—E—!!!”:GOTO60
100 JV=PEEK(56320):REM GET JOYSTICK VALUE (56320 FOR PORT2, 56321 FOR PORT1)
110 FR=JVAND16:REM FORM FIRE BUTTON STATUS
120 JV=15-(JVAND15):REM FORM DIRECTION VALUE
130 RETURN