ValidationAction action = new ValidationAction();
action.setStringValue("a string");
valueStack.push(action);
ValidatorContext context = new GenericValidatorContext(action);
RequiredStringValidator validator = new RequiredStringValidator();
validator.setValidatorContext(context);
validator.setFieldName("stringValue");
validator.setValueStack(valueStack);
// when
validator.validate(action);
// then
assertTrue(context.getFieldErrors().size() == 0);
}