diff --git a/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php
index f5c06e6e5dd7a069bd0ca2c047365f2a36f64d42..330782b0d69460701cb3e0bcfe259ed289e7fb10 100644
--- a/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php
+++ b/core/modules/datetime/src/Plugin/Field/FieldType/DateTimeItem.php
@@ -17,7 +17,8 @@
  *   description = @Translation("Create and store date values."),
  *   default_widget = "datetime_default",
  *   default_formatter = "datetime_default",
- *   list_class = "\Drupal\datetime\Plugin\Field\FieldType\DateTimeFieldItemList"
+ *   list_class = "\Drupal\datetime\Plugin\Field\FieldType\DateTimeFieldItemList",
+ *   constraints = {"DateTimeFormat" = {}}
  * )
  */
 class DateTimeItem extends FieldItemBase {
diff --git a/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraint.php b/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraint.php
new file mode 100644
index 0000000000000000000000000000000000000000..5ed340d44a4c62bc95d1500c27e50a4fd22f99e9
--- /dev/null
+++ b/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraint.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace Drupal\datetime\Plugin\Validation\Constraint;
+
+use Symfony\Component\Validator\Constraint;
+
+/**
+ * Validation constraint for DateTime items to ensure the format is correct.
+ *
+ * @Constraint(
+ *   id = "DateTimeFormat",
+ *   label = @Translation("Datetime format valid for datetime type.", context = "Validation"),
+ * )
+ */
+class DateTimeFormatConstraint extends Constraint {
+
+  /**
+   * Message for when the value isn't a string.
+   *
+   * @var string
+   */
+  public $badType = "The datetime value must be a string.";
+
+  /**
+   * Message for when the value isn't in the proper format.
+   *
+   * @var string
+   */
+  public $badFormat = "The datetime value '@value' is invalid for the format '@format'";
+
+  /**
+   * Message for when the value did not parse properly.
+   *
+   * @var string
+   */
+  public $badValue = "The datetime value '@value' did not parse properly for the format '@format'";
+
+}
diff --git a/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php b/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php
new file mode 100644
index 0000000000000000000000000000000000000000..a027a82f098491661522a29d197a15be53777437
--- /dev/null
+++ b/core/modules/datetime/src/Plugin/Validation/Constraint/DateTimeFormatConstraintValidator.php
@@ -0,0 +1,56 @@
+<?php
+
+namespace Drupal\datetime\Plugin\Validation\Constraint;
+
+use Drupal\Component\Datetime\DateTimePlus;
+use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
+use Symfony\Component\Validator\Constraint;
+use Symfony\Component\Validator\ConstraintValidator;
+
+/**
+ * Constraint validator for DateTime items to ensure the format is correct.
+ */
+class DateTimeFormatConstraintValidator extends ConstraintValidator {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validate($item, Constraint $constraint) {
+    /* @var $item \Drupal\datetime\Plugin\Field\FieldType\DateTimeItem */
+    if (isset($item)) {
+      $value = $item->getValue()['value'];
+      if (!is_string($value)) {
+        $this->context->addViolation($constraint->badType);
+      }
+      else {
+        $datetime_type = $item->getFieldDefinition()->getSetting('datetime_type');
+        $format = $datetime_type === DateTimeItem::DATETIME_TYPE_DATE ? DATETIME_DATE_STORAGE_FORMAT : DATETIME_DATETIME_STORAGE_FORMAT;
+        $date = NULL;
+        try {
+          $date = DateTimePlus::createFromFormat($format, $value, new \DateTimeZone(DATETIME_STORAGE_TIMEZONE));
+        }
+        catch (\InvalidArgumentException $e) {
+          $this->context->addViolation($constraint->badFormat, [
+            '@value' => $value,
+            '@format' => $format,
+          ]);
+          return;
+        }
+        catch (\UnexpectedValueException $e) {
+          $this->context->addViolation($constraint->badValue, [
+            '@value' => $value,
+            '@format' => $format,
+          ]);
+          return;
+        }
+        if ($date === NULL || $date->hasErrors()) {
+          $this->context->addViolation($constraint->badFormat, [
+            '@value' => $value,
+            '@format' => $format,
+          ]);
+        }
+      }
+    }
+  }
+
+}
diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..1051ce45fff15b0aff4ca27a3ebc48be10a756af
--- /dev/null
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDateonlyTest.php
@@ -0,0 +1,154 @@
+<?php
+
+namespace Drupal\Tests\datetime\Functional\EntityResource\EntityTest;
+
+use Drupal\Core\Url;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\EntityTest\EntityTestResourceTestBase;
+use GuzzleHttp\RequestOptions;
+
+/**
+ * Tests the datetime field constraint with 'date' items.
+ *
+ * @group datetime
+ */
+class EntityTestDateonlyTest extends EntityTestResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * The ISO date string to use throughout the test.
+   *
+   * @var string
+   */
+  protected static $dateString = '2017-03-01';
+
+  /**
+   * Datetime test field name.
+   *
+   * @var string
+   */
+  protected static $fieldName = 'field_dateonly';
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['datetime', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    // Add datetime field.
+    FieldStorageConfig::create([
+      'field_name' => static::$fieldName,
+      'type' => 'datetime',
+      'entity_type' => static::$entityTypeId,
+      'settings' => ['datetime_type' => DateTimeItem::DATETIME_TYPE_DATE],
+    ])
+      ->save();
+
+    FieldConfig::create([
+      'field_name' => static::$fieldName,
+      'entity_type' => static::$entityTypeId,
+      'bundle' => $this->entity->bundle(),
+      'settings' => ['default_value' => static::$dateString],
+    ])
+      ->save();
+
+    // Reload entity so that it has the new field.
+    $this->entity = $this->entityStorage->load($this->entity->id());
+    $this->entity->set(static::$fieldName, ['value' => static::$dateString]);
+    $this->entity->save();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    $entity_test = EntityTest::create([
+      'name' => 'Llama',
+      'type' => static::$entityTypeId,
+      static::$fieldName => static::$dateString,
+    ]);
+    $entity_test->setOwnerId(0);
+    $entity_test->save();
+
+    return $entity_test;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedNormalizedEntity() {
+    return parent::getExpectedNormalizedEntity() + [
+      static::$fieldName => [
+        [
+          'value' => $this->entity->get(static::$fieldName)->value,
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPostEntity() {
+    return parent::getNormalizedPostEntity() + [
+      static::$fieldName => [
+        [
+          'value' => static::$dateString,
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function assertNormalizationEdgeCases($method, Url $url, array $request_options) {
+    parent::assertNormalizationEdgeCases($method, $url, $request_options);
+
+    if ($this->entity->getEntityType()->hasKey('bundle')) {
+      $fieldName = static::$fieldName;
+
+      // DX: 422 when date type is incorrect.
+      $normalization = $this->getNormalizedPostEntity();
+      $normalization[static::$fieldName][0]['value'] = [
+        '2017', '03', '01',
+      ];
+
+      $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
+      $response = $this->request($method, $url, $request_options);
+      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value must be a string.\n{$fieldName}.0.value: This value should be of the correct primitive type.\n";
+      $this->assertResourceErrorResponse(422, $message, $response);
+
+      // DX: 422 when date format is incorrect.
+      $normalization = $this->getNormalizedPostEntity();
+      $value = '2017-03-01T01:02:03';
+      $normalization[static::$fieldName][0]['value'] = $value;
+
+      $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
+      $response = $this->request($method, $url, $request_options);
+      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value '{$value}' is invalid for the format 'Y-m-d'\n";
+      $this->assertResourceErrorResponse(422, $message, $response);
+
+      // DX: 422 when value is not a valid date.
+      $normalization = $this->getNormalizedPostEntity();
+      $value = '2017-13-55';
+      $normalization[static::$fieldName][0]['value'] = $value;
+
+      $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
+      $response = $this->request($method, $url, $request_options);
+      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value '{$value}' did not parse properly for the format 'Y-m-d'\n{$fieldName}.0.value: This value should be of the correct primitive type.\n";
+      $this->assertResourceErrorResponse(422, $message, $response);
+    }
+  }
+
+}
diff --git a/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..ffce48c340cffbcb4ef68a7c8d6bd59dfc2ad143
--- /dev/null
+++ b/core/modules/datetime/tests/src/Functional/EntityResource/EntityTest/EntityTestDatetimeTest.php
@@ -0,0 +1,154 @@
+<?php
+
+namespace Drupal\Tests\datetime\Functional\EntityResource\EntityTest;
+
+use Drupal\Core\Url;
+use Drupal\entity_test\Entity\EntityTest;
+use Drupal\datetime\Plugin\Field\FieldType\DateTimeItem;
+use Drupal\field\Entity\FieldConfig;
+use Drupal\field\Entity\FieldStorageConfig;
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\EntityTest\EntityTestResourceTestBase;
+use GuzzleHttp\RequestOptions;
+
+/**
+ * Tests the datetime field constraint with 'datetime' items.
+ *
+ * @group datetime
+ */
+class EntityTestDatetimeTest extends EntityTestResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * The ISO date string to use throughout the test.
+   *
+   * @var string
+   */
+  protected static $dateString = '2017-03-01T20:02:00';
+
+  /**
+   * Datetime test field name.
+   *
+   * @var string
+   */
+  protected static $fieldName = 'field_datetime';
+
+  /**
+   * {@inheritdoc}
+   */
+  public static $modules = ['datetime', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public function setUp() {
+    parent::setUp();
+
+    // Add datetime field.
+    FieldStorageConfig::create([
+      'field_name' => static::$fieldName,
+      'type' => 'datetime',
+      'entity_type' => static::$entityTypeId,
+      'settings' => ['datetime_type' => DateTimeItem::DATETIME_TYPE_DATETIME],
+    ])
+      ->save();
+
+    FieldConfig::create([
+      'field_name' => static::$fieldName,
+      'entity_type' => static::$entityTypeId,
+      'bundle' => $this->entity->bundle(),
+      'settings' => ['default_value' => static::$dateString],
+    ])
+      ->save();
+
+    // Reload entity so that it has the new field.
+    $this->entity = $this->entityStorage->load($this->entity->id());
+    $this->entity->set(static::$fieldName, ['value' => static::$dateString]);
+    $this->entity->save();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    $entity_test = EntityTest::create([
+      'name' => 'Llama',
+      'type' => static::$entityTypeId,
+      static::$fieldName => static::$dateString,
+    ]);
+    $entity_test->setOwnerId(0);
+    $entity_test->save();
+
+    return $entity_test;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedNormalizedEntity() {
+    return parent::getExpectedNormalizedEntity() + [
+      static::$fieldName => [
+        [
+          'value' => $this->entity->get(static::$fieldName)->value,
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPostEntity() {
+    return parent::getNormalizedPostEntity() + [
+      static::$fieldName => [
+        [
+          'value' => static::$dateString,
+        ],
+      ],
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function assertNormalizationEdgeCases($method, Url $url, array $request_options) {
+    parent::assertNormalizationEdgeCases($method, $url, $request_options);
+
+    if ($this->entity->getEntityType()->hasKey('bundle')) {
+      $fieldName = static::$fieldName;
+
+      // DX: 422 when date type is incorrect.
+      $normalization = $this->getNormalizedPostEntity();
+      $normalization[static::$fieldName][0]['value'] = [
+        '2017', '03', '01', '21', '53', '00',
+      ];
+
+      $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
+      $response = $this->request($method, $url, $request_options);
+      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value must be a string.\n{$fieldName}.0.value: This value should be of the correct primitive type.\n";
+      $this->assertResourceErrorResponse(422, $message, $response);
+
+      // DX: 422 when date format is incorrect.
+      $normalization = $this->getNormalizedPostEntity();
+      $value = '2017-03-01';
+      $normalization[static::$fieldName][0]['value'] = $value;
+
+      $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
+      $response = $this->request($method, $url, $request_options);
+      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value '{$value}' is invalid for the format 'Y-m-d\\TH:i:s'\n";
+      $this->assertResourceErrorResponse(422, $message, $response);
+
+      // DX: 422 when date format is incorrect.
+      $normalization = $this->getNormalizedPostEntity();
+      $value = '2017-13-55T20:02:00';
+      $normalization[static::$fieldName][0]['value'] = $value;
+
+      $request_options[RequestOptions::BODY] = $this->serializer->encode($normalization, static::$format);
+      $response = $this->request($method, $url, $request_options);
+      $message = "Unprocessable Entity: validation failed.\n{$fieldName}.0: The datetime value '{$value}' did not parse properly for the format 'Y-m-d\\TH:i:s'\n{$fieldName}.0.value: This value should be of the correct primitive type.\n";
+      $this->assertResourceErrorResponse(422, $message, $response);
+    }
+  }
+
+}
diff --git a/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php b/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php
index e28667f0725f86bb947228371d5f5d7be410404a..98840078cb759cacfce072a2cf5dcc2753b77f7e 100644
--- a/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php
+++ b/core/modules/datetime/tests/src/Kernel/DateTimeItemTest.php
@@ -80,16 +80,19 @@ public function testDateTime() {
     $this->assertTrue($entity->field_datetime[0] instanceof FieldItemInterface, 'Field item implements interface.');
     $this->assertEqual($entity->field_datetime->value, $value);
     $this->assertEqual($entity->field_datetime[0]->value, $value);
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Verify changing the date value.
     $new_value = '2016-11-04T00:21:00';
     $entity->field_datetime->value = $new_value;
     $this->assertEqual($entity->field_datetime->value, $new_value);
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Read changed entity and assert changed values.
     $this->entityValidateAndSave($entity);
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime->value, $new_value);
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test the generateSampleValue() method.
     $entity = EntityTest::create();
@@ -118,16 +121,19 @@ public function testDateOnly() {
     $this->assertTrue($entity->field_datetime[0] instanceof FieldItemInterface, 'Field item implements interface.');
     $this->assertEqual($entity->field_datetime->value, $value);
     $this->assertEqual($entity->field_datetime[0]->value, $value);
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Verify changing the date value.
     $new_value = '2016-11-04';
     $entity->field_datetime->value = $new_value;
     $this->assertEqual($entity->field_datetime->value, $new_value);
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Read changed entity and assert changed values.
     $this->entityValidateAndSave($entity);
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime->value, $new_value);
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test the generateSampleValue() method.
     $entity = EntityTest::create();
@@ -152,6 +158,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with string value.');
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test DateTimeItem::setValue() using property array.
     $entity = EntityTest::create();
@@ -162,6 +169,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with array value.');
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test a date-only field.
     $this->fieldStorage->setSetting('datetime_type', DateTimeItem::DATETIME_TYPE_DATE);
@@ -176,6 +184,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with string value.');
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test DateTimeItem::setValue() using property array.
     $entity = EntityTest::create();
@@ -186,6 +195,7 @@ public function testSetValue() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, 'DateTimeItem::setValue() works with array value.');
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
   }
 
   /**
@@ -205,6 +215,7 @@ public function testSetValueProperty() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, '"Value" property can be set directly.');
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
 
     // Test Date::setValue() with a date-only field.
     // Test a date+time field.
@@ -219,6 +230,107 @@ public function testSetValueProperty() {
     $id = $entity->id();
     $entity = EntityTest::load($id);
     $this->assertEqual($entity->field_datetime[0]->value, $value, '"Value" property can be set directly.');
+    $this->assertEquals(DATETIME_STORAGE_TIMEZONE, $entity->field_datetime->date->getTimeZone()->getName());
+  }
+
+  /**
+   * Tests the constraint validations for fields with date and time.
+   *
+   * @dataProvider datetimeValidationProvider
+   */
+  public function testDatetimeValidation($value) {
+    $this->setExpectedException(\PHPUnit_Framework_AssertionFailedError::class);
+
+    $this->fieldStorage->setSetting('datetime_type', DateTimeItem::DATETIME_TYPE_DATETIME);
+    $this->fieldStorage->save();
+    $entity = EntityTest::create();
+
+    $entity->set('field_datetime', $value);
+    $this->entityValidateAndSave($entity);
+  }
+
+  /**
+   * Provider for testDatetimeValidation().
+   */
+  public function datetimeValidationProvider() {
+    return [
+      // Valid ISO 8601 dates, but unsupported by DateTimeItem.
+      ['2014-01-01T20:00:00Z'],
+      ['2014-01-01T20:00:00+04:00'],
+      ['2014-01-01T20:00:00+0400'],
+      ['2014-01-01T20:00:00+04'],
+      ['2014-01-01T20:00:00.123'],
+      ['2014-01-01T200000'],
+      ['2014-01-01T2000'],
+      ['2014-01-01T20'],
+      ['20140101T20:00:00'],
+      ['2014-01T20:00:00'],
+      ['2014-001T20:00:00'],
+      ['2014001T20:00:00'],
+      // Valid date strings, but unsupported by DateTimeItem.
+      ['2016-11-03 20:52:00'],
+      ['Thu, 03 Nov 2014 20:52:00 -0400'],
+      ['Thursday, November 3, 2016 - 20:52'],
+      ['Thu, 11/03/2016 - 20:52'],
+      ['11/03/2016 - 20:52'],
+      // Invalid date strings.
+      ['YYYY-01-01T20:00:00'],
+      ['2014-MM-01T20:00:00'],
+      ['2014-01-DDT20:00:00'],
+      ['2014-01-01Thh:00:00'],
+      ['2014-01-01T20:mm:00'],
+      ['2014-01-01T20:00:ss'],
+      // Invalid dates.
+      ['2014-13-13T20:00:00'],
+      ['2014-01-55T20:00:00'],
+      ['2014-01-01T25:00:00'],
+      ['2014-01-01T00:70:00'],
+      ['2014-01-01T00:00:70'],
+      // Proper format for different field setting.
+      ['2014-01-01'],
+      // Wrong input type.
+      [['2014', '01', '01', '00', '00', '00']],
+    ];
+  }
+
+  /**
+   * Tests the constraint validations for fields with date only.
+   *
+   * @dataProvider dateonlyValidationProvider
+   */
+  public function testDateonlyValidation($value) {
+    $this->setExpectedException(\PHPUnit_Framework_AssertionFailedError::class);
+
+    $this->fieldStorage->setSetting('datetime_type', DateTimeItem::DATETIME_TYPE_DATE);
+    $this->fieldStorage->save();
+    $entity = EntityTest::create();
+
+    $entity->set('field_datetime', $value);
+    $this->entityValidateAndSave($entity);
+  }
+
+  /**
+   * Provider for testDatetimeValidation().
+   */
+  public function dateonlyValidationProvider() {
+    return [
+      // Valid date strings, but unsupported by DateTimeItem.
+      ['Thu, 03 Nov 2014'],
+      ['Thursday, November 3, 2016'],
+      ['Thu, 11/03/2016'],
+      ['11/03/2016'],
+      // Invalid date strings.
+      ['YYYY-01-01'],
+      ['2014-MM-01'],
+      ['2014-01-DD'],
+      // Invalid dates.
+      ['2014-13-01'],
+      ['2014-01-55'],
+      // Proper format for different field setting.
+      ['2014-01-01T20:00:00'],
+      // Wrong input type.
+      [['2014', '01', '01']],
+    ];
   }
 
 }