pub async fn test_pool() -> ConnectionPool<DB> {
        const DEFAULT_CONNECTIONS: u32 = 100; // Expected to be enough for any unit test.
        Self::constrained_test_pool(DEFAULT_CONNECTIONS).await
    }
Creates a test pool with a reasonably large number of connections.

Test pools trace their active connections. If acquiring a connection fails (e.g., with a timeout),
the returned error will contain information on all active connections.
core/lib/db_connection/src/connection_pool.rs