Update BUILD

Test automatic import to Piper.

tests/BUILD

diff --git a/tests/BUILD b/tests/BUILD
index 2381713..a0baa9d 100644
--- a/tests/BUILD
+++ b/tests/BUILD
@@ -1,5 +1,7 @@
 load("//proto:defs.bzl", "proto_library")
 
+# Test automatic import.
+
 proto_library(
     name = "empty_proto",
     srcs = [