diff --git a/tests/utmp_test.cpp b/tests/utmp_test.cpp
index b024818..459f9c3 100644
--- a/tests/utmp_test.cpp
+++ b/tests/utmp_test.cpp
@@ -25,6 +25,7 @@
 }
 
 TEST(utmp, smoke) {
+  // The rest of <utmp.h> is just no-op implementations, so testing is trivial.
   ASSERT_EQ(-1, utmpname("hello"));
   setutent();
   ASSERT_EQ(NULL, getutent());