Add a build_test rule. (#97)

* Add a build_test rule.

This rules (marco) provides a 'test' target that can be used to ensure other
targets build.
diff --git a/tests/BUILD b/tests/BUILD
index 8657cae..fdf00ad 100644
--- a/tests/BUILD
+++ b/tests/BUILD
@@ -1,3 +1,4 @@
+load(":build_test_tests.bzl", "build_test_test_suite")
 load(":collections_tests.bzl", "collections_test_suite")
 load(":dicts_tests.bzl", "dicts_test_suite")
 load(":maprule_tests.bzl", "maprule_test_suite")
@@ -13,6 +14,8 @@
 
 licenses(["notice"])
 
+build_test_test_suite()
+
 collections_test_suite()
 
 dicts_test_suite()