Add TEST_MAPPING.

Just libhidl_test for now which is a simple unit test that doesn't
usually get run.

Test: N/A
Change-Id: I54a8fd120ddf0b4672f4ccb6b07a94c51970ca5b
diff --git a/TEST_MAPPING b/TEST_MAPPING
new file mode 100644
index 0000000..3e17fc4
--- /dev/null
+++ b/TEST_MAPPING
@@ -0,0 +1,8 @@
+{
+  "presubmit": [
+    {
+      "name": "libhidl_test"
+    }
+  ]
+}
+