prepareStatement with a closed connection

Hi,

I am using the MariaDB ConnectorJ to connect to a database. Since I had several nasty problems in the past, I created some tests with JUnit to test the database connection.

Since many versions of Connector/J this test fails, no exception is thrown (sorry, had no time to report it earlier):

	@Test

	public void constructorClosedConnection() throws SQLException {

		assertThrows(SQLException.class, () -> {

			Connection closedConnection = Database.getInstance().getConnection();

			closedConnection.rollback();

			closedConnection.close();

			closedConnection.prepareStatement("SELECT * FROM SampleTable");

		});

	}

The function Database.getInstance().getConnection() grabs a connection from the connection-pool and returns it. This issue is not important in production, but every time I run my tests this test fails, while it worked in the past.