add set-box! tests

Author: AlexKnauth

typed-racket-test/unit-tests/typecheck-tests.rkt

@@ -1337,6 +1337,11 @@
               (-box -Nat -Int)]
         [tc-e (unbox (if (zero? (random 2)) ((inst box Natural) 3) ((inst box Integer) -5)))
               -Int]
+        [tc-e (set-box!
+               (if (zero? (random 2)) ((inst box Natural) 3) ((inst box Integer) -5))
+               1)
+              -Void]
+        [tc-err (set-box! (if (zero? (random 2)) ((inst box Natural) 3) ((inst box Integer) -5)) -1)]
         [tc-e (floor 1/2) -Nat]
         [tc-e (ceiling 1/2) -PosInt]
         [tc-e (truncate 0.5) -NonNegFlonum]