test/multiwaiter: check that we clean up correctly

tests/multiwaiter-test.cc

diff --git a/tests/multiwaiter-test.cc b/tests/multiwaiter-test.cc
index d9d99e9..b6b77dd 100644
--- a/tests/multiwaiter-test.cc
+++ b/tests/multiwaiter-test.cc
@@ -126,6 +126,7 @@
 	     "Queue reports ready to receive but should be empty.");
 	TEST(events[1].value == 1, "Futex reports no wake");
 
-	multiwaiter_delete(MALLOC_CAPABILITY, mw);
+	TEST_EQUAL(
+	  multiwaiter_delete(MALLOC_CAPABILITY, mw), 0, "Failed to clean up");
 	return 0;
 }