@Test
    public void testConnectorHasMissingTransformClass() throws InterruptedException {
        Map<String, String> config = defaultSinkConnectorProps();
        String transformName = "t";
        config.put(TRANSFORMS_CONFIG, transformName);
        config.put(TRANSFORMS_CONFIG + "." + transformName + ".type", "WheresTheFruit");
        connect.assertions().assertExactlyNumErrorsOnConnectorConfigValidation(
                config.get(CONNECTOR_CLASS_CONFIG),
                config,
                1,
                "Connector config should fail preflight validation when a transformation with a class not found on the worker is specified",
                0
        );
    }
Integration test for preflight connector config validation
connect/runtime/src/test/java/org/apache/kafka/connect/integration/ConnectorValidationIntegrationTest.java