diff --git a/assets/README b/assets/README
index ad6a29c..43b0965 100644
--- a/assets/README
+++ b/assets/README
@@ -10,3 +10,50 @@
 DO NOT MANUALLY EDIT THIS FILE
 
 This file defines carrier id and should be single versioned.
+
+===== How to test carrier id locally =====
+
+If you want to make change locally during testing, currently there are two ways:
+
+1. Modify carrierIdentification.db database by SQL command
+
+For example (Insert MCCMNC '12345' and gid1 'test' to carrier id 20000):
+```
+$ adb shell
+device:/ $ su
+device:/ # DB='/data/user_de/0/com.android.providers.telephony/databases/carrierIdentification.db'
+device:/ # sqlite3 $DB "INSERT INTO carrier_id(mccmnc, gid1, carrier_id, carrier_name) VALUES (12345, 'test', 20000, 'test_carrier')"
+device:/ # reboot
+```
+
+2. Override carrier_list.pb
+
+- Modify carrier_list.textpb directly (Note: You should also bump the version
+  number to let TelephonyProvider reload the carrier_list.pb)
+- Generate class file by using the carrier id proto(TelephonyProvider/proto/src/carrierId.proto)
+  (See https://developers.google.com/protocol-buffers/docs/overview#generating)
+- Create a converter by using TextFormat tool to convert textpb to pb
+  (Text Format: https://developers.google.com/protocol-buffers/docs/reference/java/com/google/protobuf/TextFormat)
+- Rename file to carrier_list_test.pb and push the output file to
+    /data/user_de/0/com.android.providers.telephony/files/carrier_list_test.pb
+- Reboot the device
+
+Converter example:
+```
+#!/usr/bin/env python3
+from google.protobuf import text_format
+
+# Generated by: protoc -I=./ --python_out=./ ./carrierId.proto
+from carrierId_pb2 import CarrierList
+
+def main():
+  with open("carrier_list.textpb", "r") as rd:
+    carrierList = CarrierList()
+    text_format.Merge(rd.read(), carrierList)
+
+    with open("carrier_list.pb", "wb") as wf:
+      wf.write(carrierList.SerializeToString())
+
+if __name__ == '__main__':
+  main()
+```
diff --git a/src/com/android/providers/telephony/CarrierIdProvider.java b/src/com/android/providers/telephony/CarrierIdProvider.java
index a3c299f..3e751aa 100644
--- a/src/com/android/providers/telephony/CarrierIdProvider.java
+++ b/src/com/android/providers/telephony/CarrierIdProvider.java
@@ -83,6 +83,9 @@
     private static final int VERSION_BITMASK = 0x00FFFFFF;
     private static final String OTA_UPDATED_PB_PATH = "misc/carrierid/" + ASSETS_PB_FILE;
     private static final String PREF_FILE = CarrierIdProvider.class.getSimpleName();
+    // For testing purposes only.
+    private static final String OVERRIDE_PB_PATH =
+            "/data/user_de/0/com.android.providers.telephony/files/carrier_list_test.pb";
 
     private static final UriMatcher s_urlMatcher = new UriMatcher(UriMatcher.NO_MATCH);
 
@@ -527,9 +530,14 @@
         CarrierIdProto.CarrierList assets = null;
         CarrierIdProto.CarrierList ota = null;
         InputStream is = null;
+        File testFile = new File(OVERRIDE_PB_PATH);
 
         try {
-            is = getContext().getAssets().open(ASSETS_PB_FILE);
+            if (Build.IS_DEBUGGABLE && testFile.exists()) {
+                is = new FileInputStream(testFile);
+            } else {
+                is = getContext().getAssets().open(ASSETS_PB_FILE);
+            }
             assets = CarrierIdProto.CarrierList.parseFrom(readInputStreamToByteArray(is));
         } catch (IOException ex) {
             Log.e(TAG, "read carrier list from assets pb failure: " + ex);