--- /dev/null
+<?php
+
+namespace Drupal\entity_test\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Validates the FieldWidgetConstraint constraint.
+ */
+class FieldWidgetConstraintValidator extends ConstraintValidator {
+
+ /**
+ * {@inheritdoc}
+ */
+ public function validate($field_item, Constraint $constraint) {
+ $this->context->addViolation($constraint->message);
+ }
+
+}