Run update_engine_unittests on presubmit am: fbfe4c35db

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/2029098

Change-Id: Id6611e6bb7245ad771c97e5fc92dfad02e67d09b
diff --git a/TEST_MAPPING b/TEST_MAPPING
new file mode 100644
index 0000000..93777d4
--- /dev/null
+++ b/TEST_MAPPING
@@ -0,0 +1,7 @@
+{
+  "presubmit": [
+    {
+      "name": "update_engine_unittests"
+    }
+  ]
+}