### Question:
DMNClientDiagramValidator extends ClientDiagramValidator { ErrorCallback<Object> onValidatorError() { return (msg, error) -> { logError("Validation service error"); return false; }; } protected  DMNClientDiagramValidator(); @Inject  DMNClientDiagramValidator(final DefinitionManager definitionManager,
                                     final RuleManager ruleManager,
                                     final TreeWalkTraverseProcessor treeWalkTraverseProcessor,
                                     final ModelValidator modelValidator,
                                     final ManagedInstance<DomainValidator> validators,
                                     final Caller<DMNDomainValidator> dmnDomainValidator,
                                     final DMNMarshallerService dmnMarshallerService); @Override void validate(final Diagram diagram,
                         final Consumer<Collection<DiagramElementViolation<RuleViolation>>> resultConsumer);  }### Answer:
@Test public void testOnValidatorError() { doNothing().when(validator).logError(anyString()); validator.onValidatorError().error(null, null); verify(validator).logError("Validation service error"); }