rackunit: prevent test case from killing test-runner thread

closes PR 11586

original commit: a100395626c0e7f569ddc301ac4d57cbc6f4607a

collects/rackunit/private/test-case.rkt

@@ -26,7 +26,8 @@
 ;; Run a test-case immediately, printing information on failure
 (define (default-test-case-around thunk)
   (with-handlers ([(lambda (e) #t) default-test-case-handler])
-    (thunk)))
+    (parameterize ((current-custodian (make-custodian)))
+      (thunk))))
 
 ;; default-test-case-handler : any -> any
 (define (default-test-case-handler e)

collects/rackunit/text-ui.rkt

@@ -216,6 +216,7 @@
 
 ;; run-tests : test [(U 'quiet 'normal 'verbose)] -> integer
 (define (run-tests test [mode 'normal])
+  (parameterize ((current-custodian (make-custodian)))
     (monad-value
      ((compose
        (sequence*
@@ -239,4 +240,4 @@
         ((normal) (std-test/text-ui display-context test))
         ((verbose) (std-test/text-ui
                     (lambda (x) (display-context x #t))
-                  test))))))
+                    test)))))))

collects/tests/rackunit/text-ui-test.rkt

@@ -220,5 +220,19 @@
                (check = foo 2)))
              'verbose)
             (check = foo 3)))))
-   ))
 
+   (test-case
+    "cannot kill current thread in test case"
+    (check-equal? (call-in-nested-thread
+                   (lambda ()
+                     (with-silent-output
+                      (lambda ()
+                        (run-tests
+                         (test-suite "tests"
+                           (test-case "kill-thread"
+                             (kill-thread (current-thread)))))))))
+                  ;; If the kill-thread were successful, call-in-nested-thread
+                  ;; would raise error. We expect kill-thread to raise error,
+                  ;; caught by run-tests.
+                  1))
+   ))