diff --git a/src/testing/testing.go b/src/testing/testing.go
index eeee0aac17..681f99ef93 100644
--- a/src/testing/testing.go
+++ b/src/testing/testing.go
@@ -233,6 +233,8 @@
 //		os.Exit(m.Run())
 //	}
 //
+// TestMain is a low-level primitive and should not be necessary for casual
+// testing needs, where ordinary test functions suffice.
 package testing
 
 import (