You're returning a boolean (True/False), not the number in negative form.

Nope, the lines . . ;

Test Passed: Value == z
... last argument - Expected: z, instead got: a

. . . or . . .

Test Passed: Value == c
... last argument - Expected: c, instead got: a

result from distinct tests.

Test Passed: Value == z
Test Passed: Value == c

. . . (which succeeded) are about last char of strings.

... last argument - Expected: z, instead got: a
... last argument - Expected: z, instead got: a

. . . (which failed) are about last argument of arguments.

eg, in :

last( arg1, arg2, arg3, ..., arg99 )

. . . last should return arg99 'cause it's the last argument.

Hope it helps.
; )