private void verifySslConfigs(Args args) throws Exception {
        server = createEchoServer(args, SecurityProtocol.SSL);
        createSelector(args.sslClientConfigs);
        InetSocketAddress addr = new InetSocketAddress("localhost", server.port());
        String node = "0";
        selector.connect(node, addr, BUFFER_SIZE, BUFFER_SIZE);
        NetworkTestUtils.checkClientConnection(selector, node, 100, 10);
    }
Tests invalid ssl.engine.factory plugin class
clients/src/test/java/org/apache/kafka/common/network/SslTransportLayerTest.java