@Test
    public void testConnectorHasConverterWithNoSuitableConstructor() throws InterruptedException {
        Map<String, String> config = innocuousSinkConnectorProps();
        config.put(
                KEY_CONVERTER_CLASS_CONFIG,
                TestPlugins.TestPlugin.BAD_PACKAGING_NO_DEFAULT_CONSTRUCTOR_CONVERTER.className()
        );
        connect.assertions().assertExactlyNumErrorsOnConnectorConfigValidation(
                config.get(CONNECTOR_CLASS_CONFIG),
                config,
                1,
                "Connector config should fail preflight validation when a converter class with no suitable constructor is specified",
                0
        );
    }
Integration test for preflight connector config validation
connect/runtime/src/test/java/org/apache/kafka/connect/integration/ConnectorValidationIntegrationTest.java