Validate Entity D8

validate.php

<?php
$errors = array();
$validate = $entity->validate();
$violations = $validate->getIterator();

foreach ($violations as $violation) {
  $constraint = get_class($violation->getConstraint());
  $type = $constraint;
  $msg = $violation->getMessageTemplate();
  if ($constraint == 'Drupal\Core\Validation\Plugin\Validation\Constraint\NotNullConstraint') {
    $type = 'required';
    $msg = t('This field is required');
  }

  $path = $violation->getPropertyPath();
  $path = explode('.', $path);

  /* @var $violation \Symfony\Component\Validator\ConstraintViolation */
  $errors[] = array(
    'field' => $path[0],
    'type' => $type,
    'msg' => $msg,
  );
}