Update DEVELOPER.md (#200)

Co-authored-by: Wenxin Du <117315983+duwenxin99@users.noreply.github.com>

Author: averikitsch

DEVELOPER.md

@@ -18,14 +18,22 @@ Learn more by reading [How should I write my commits?](https://github.com/google
 
 ### Run tests locally
 
-1. Set environment variables for `INSTANCE_ID`, `DATABASE_ID`, `REGION`, `DB_USER`, `DB_PASSWORD`
+1. Set environment variables for `INSTANCE_ID`, `DATABASE_ID`, `REGION`, `DB_USER`, `DB_PASSWORD`, `IAM_ACCOUNT`.
 
 1. Run pytest to automatically run all tests:
 
     ```bash
     pytest
     ```
 
+Notes:
+
+* Tests use both IAM and built-in authentication. 
+  * Learn how to set up a built-in databases user at [Cloud SQL built-in database authentication](https://cloud.google.com/sql/docs/postgres/built-in-authentication).
+  * Local tests will run against your `gcloud` credentials. Use `gcloud` to login with your personal account or a service account. This account will be used to run IAM tests. Learn how to set up access to the database at [Manage users with IAM database authentication](https://cloud.google.com/sql/docs/postgres/add-manage-iam-users). The "IAM_ACCOUNT" environment variable is also used to test authentication to override the local account. A personal account or a service account can be used for this test.
+  * You may need to grant access to the public schema for your new database user: `GRANT ALL ON SCHEMA public TO myaccount@example.com;`
+
+
 ### CI Platform Setup
 
 Cloud Build is used to run tests against Google Cloud resources in test project: langchain-cloud-sql-testing.
@@ -121,4 +129,4 @@ The kokoro docs pipeline runs when a new release is created. See `.kokoro/` for
 [triggers]: https://console.cloud.google.com/cloud-build/triggers?e=13802955&project=langchain-cloud-sql-testing
 [vectorstore]: https://github.com/googleapis/langchain-google-cloud-sql-pg-python/tree/main/docs/vector_store.ipynb
 [loader]: https://github.com/googleapis/langchain-google-cloud-sql-pg-python/tree/main/docs/document_loader.ipynb
-[history]: https://github.com/googleapis/langchain-google-cloud-sql-pg-python/tree/main/docs/chat_message_history.ipynb
+[history]: https://github.com/googleapis/langchain-google-cloud-sql-pg-python/tree/main/docs/chat_message_history.ipynb