[#30411] YSQL: Fix TestReserveYsqlInternalConns test on running with conn mgr

Summary: This diff fixes `org.yb.ysqlconnmgr.TestReserveYsqlInternalConns` when ran with `--enable-ysql-conn-mgr-test` flag. Before running the test, internal set-up creates physical connection to default user/db (yugabyte/yugabyte). Therefore on running the test for different pool, it reduces number of available backends from total `ysql_max_connections`. This diff overrides `verifyClusterAcceptsPGConnections` function to create internal set-up connections to PG so they get successfully closed.

Test Plan:
Jenkins: enable connection manager, test regex: .*ReserveYsqlInternalConns.*

Make sure test passes with conn mgr flag:
`./yb_build.sh --enable-ysql-conn-mgr-test --java-test org.yb.ysqlconnmgr.TestReserveYsqlInternalConns`

Reviewers: skumar, arpit.saxena

Reviewed By: arpit.saxena

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D50687

Author: Manav Kumar

java/yb-ysql-conn-mgr/src/test/java/org/yb/ysqlconnmgr/TestReserveYsqlInternalConns.java

@@ -24,6 +24,7 @@
 
 import org.junit.Test;
 import org.junit.runner.RunWith;
+import org.yb.client.TestUtils;
 import org.yb.minicluster.MiniYBClusterBuilder;
 import org.yb.pgsql.ConnectionEndpoint;
 
@@ -59,6 +60,25 @@ protected void customizeMiniClusterBuilder(MiniYBClusterBuilder builder) {
             "superuser_reserved_connections=" + RESERVED_CONNS_FOR_NON_REPLICATION_SUPERUSER);
     }
 
+    // Before starting the test, avoid making connection to conn mgr end point
+    // even when test is ran with --enable-ysql-conn-mgr flag.
+    // Otherwise it creates extra backend to default user / db which limits number
+    // of connection to other user/db & can cause test to fail.
+    @Override
+    public void verifyClusterAcceptsPGConnections() throws Exception {
+        LOG.info("Waiting for the cluster to accept pg connections");
+        TestUtils.waitFor(() -> {
+            try {
+            connectionBuilderForVerification(getConnectionBuilder())
+            .withConnectionEndpoint(ConnectionEndpoint.POSTGRES)
+            .connect().close();
+            return true;
+        } catch (Exception e) {
+            return false;
+        }
+    }, 10000);
+    }
+
     private void createUser(String userName) throws Exception {
         try (Connection conn = getConnectionBuilder()
                     .withConnectionEndpoint(ConnectionEndpoint.POSTGRES)