[OSS-ONLY] Add instructions for running JDBC tests with single-db mig…

…ration mode (#2942)

This commit adds instructions for running JDBC tests with single-db migration mode.

Signed-off-by: Sumit Jaiswal [email protected]
Co-authored-by: Sumit Jaiswal <[email protected]>

test/JDBC/README.md

@@ -20,6 +20,7 @@ The JDBC test framework for Babelfish uses the JDBC Driver for SQL Server for da
 - [Adding the test cases](#adding-the-test-cases)
 - [Reading the console output and diff](#reading-the-console-output-and-diff)
 - [Running Tests with Parallel Query Enabled](#running-tests-with-parallel-query-enabled)
+- [Running Tests with Single-DB Migration Mode](#running-tests-with-single-db-migration-mode)
 - [Running Tests with Non Default Server Collation](#running-tests-with-non-default-server-collation)
 - [Running Tests with Non Default Database Collation](#running-tests-with-non-default-database-collation)
 
@@ -463,6 +464,41 @@ After building the modified PostgreSQL engine and Babelfish extensions using the
    ```
 If you encounter failing or crashing tests in the "JDBC tests with parallel query" GitHub workflow, consider adding the names of these problematic test cases to the `parallel_query_jdbc_schedule` file. Prefix these test case names with `ignore#!#`. As we work towards resolving these issues in the future, we will gradually remove these excluded tests from the `parallel_query_jdbc_schedule` scheduling file.
 
+## Running Tests with Single-DB Migration Mode
+
+After building the modified PostgreSQL engine and Babelfish extensions using the [online instructions](../../contrib/README.md), you must:
+1. Create a PostgreSQL database and initialize Babelfish extensions with single-db migration mode by adding following line in `postgres/data/postgresql.conf` and restart engine, then initialize Babelfish extensions using the [online instructions](../../contrib/README.md)
+
+   ```bash
+   babelfishpg_tsql.migration_mode = 'single-db'
+    ```
+2. Before running JDBC tests, set the `isSingleDbMode` environment variable to `true`:
+
+   ```bash
+    export isSingleDbMode=true
+    # Verify if isSingleDbMode is set to true
+    echo $isSingleDbMode
+   ```
+3. Now Run the tests:
+    ```bash
+    mvn test
+    ```
+4. How to add expected output for some test
+    1. By default expected output of a test should be added into `expected` folder.
+    2. If the expected output is different for single-db migration mode compared to multi-db migration mode, one can add a different expected output specially for single-db migration mode in `expected/single_db/` folder. Additionally, one needs to add `-- single_db_mode_expected` flag in the corresponding input file.
+    
+5. To exclude some tests from running via the JDBC in single-db migration mode, you can add test-case name with prefix `ignore#!#` in `singledb_jdbc_schedule` file.
+
+6. Cleanup all the objects, users, roles and databases created while running the tests:
+    ```bash
+    ./cleanup.sh
+    ```
+7. Please note that whenever you had changed the migration mode and reinitialised Babelfish extensions. Update the `isSingleDbMode` environment variable with appropriate value and unset when migration mode is set to 'multi-db'.
+    ```bash
+    unset isSingleDbMode
+    ```
+    This ensures that correct expected output is picked for current migration mode.
+
 ## Running Tests with Non Default Server Collation
 
 After building the modified PostgreSQL engine and Babelfish extensions using the [online instructions](../../contrib/README.md), you must: