Added test module for testing entity contraints with Layout Paragraphs.

tests/modules/layout_paragraphs_entity_validator_test/layout_paragraphs_entity_validator_test.info.yml

+name: Layout Paragraphs Entity Validator Test
+description: Helps test custom entity validators on paragraphs
+package: Testing
+type: module
+core_version_requirement: ^9.1 || ^10

tests/modules/layout_paragraphs_entity_validator_test/layout_paragraphs_entity_validator_test.module

+<?php
+
+/**
+ * Implements hook_entity_type_alter().
+ *
+ * @param array $entity_types
+ */
+function layout_paragraphs_entity_validator_test_entity_type_alter(array &$entity_types) {
+  // Add validation constraint to the paragraph entity
+  $entity_types['paragraph']->addConstraint('LayoutParagraphsTestConstraint');
+}

tests/modules/layout_paragraphs_entity_validator_test/src/Plugin/Validation/Constraint/LayoutParagraphsTestConstraint.php

+<?php
+
+namespace Drupal\layout_paragraphs_entity_validator_test\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Checks that the submitted value is a unique integer.
+ *
+ * @Constraint(
+ *   id = "LayoutParagraphsTestConstraint",
+ *   label = @Translation("Layout Paragraphs Test Constraint", context = "Validation"),
+ *   type = "string"
+ * )
+ */
+class LayoutParagraphsTestConstraint extends Constraint {
+
+  public $message = 'Failed Layout Paragraphs test validation.';
+
+}

tests/modules/layout_paragraphs_entity_validator_test/src/Plugin/Validation/Constraint/LayoutParagraphsTestConstraintValidator.php

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