.../Rest/EntityTestMapFieldJsonAnonTest.php        | 24 +++++++++
 .../Rest/EntityTestMapFieldResourceTestBase.php}   | 63 ++++++++++++----------
 2 files changed, 58 insertions(+), 29 deletions(-)

diff --git a/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php
new file mode 100644
index 0000000..0440680
--- /dev/null
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldJsonAnonTest.php
@@ -0,0 +1,24 @@
+<?php
+
+namespace Drupal\Tests\entity_test\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class EntityTestMapFieldJsonAnonTest extends EntityTestMapFieldResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+}
diff --git a/core/modules/rest/tests/src/Functional/EntityResource/EntityTest/EntityTestMapItemNormalizerTest.php b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldResourceTestBase.php
similarity index 78%
rename from core/modules/rest/tests/src/Functional/EntityResource/EntityTest/EntityTestMapItemNormalizerTest.php
rename to core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldResourceTestBase.php
index f7386da..dcc12b9 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/EntityTest/EntityTestMapItemNormalizerTest.php
+++ b/core/modules/system/tests/modules/entity_test/tests/src/Functional/Rest/EntityTestMapFieldResourceTestBase.php
@@ -1,30 +1,39 @@
 <?php
 
-namespace Drupal\Tests\rest\Functional\EntityResource\EntityTest;
+namespace Drupal\Tests\entity_test\Functional\Rest;
 
+use Drupal\entity_test\Entity\EntityTest;
 use Drupal\entity_test\Entity\EntityTestMapField;
-use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\BcTimestampNormalizerUnixTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\EntityResourceTestBase;
+use Drupal\Tests\Traits\ExpectDeprecationTrait;
 use Drupal\user\Entity\User;
 
-/**
- * Test that MapItem are correctly exposed in REST.
- *
- * @group rest
- */
-class EntityTestMapItemNormalizerTest extends EntityTestResourceTestBase {
+abstract class EntityTestMapFieldResourceTestBase extends EntityResourceTestBase {
 
-  use AnonResourceTestTrait;
+  use BcTimestampNormalizerUnixTestTrait;
+  use ExpectDeprecationTrait;
 
   /**
    * {@inheritdoc}
    */
-  protected static $format = 'json';
+  public static $modules = ['entity_test'];
 
   /**
    * {@inheritdoc}
    */
   protected static $entityTypeId = 'entity_test_map_field';
 
+  /**
+   * {@inheritdoc}
+   */
+  protected static $patchProtectedFieldNames = [];
+
+  /**
+   * @var \Drupal\entity_test\Entity\EntityTestMapField
+   */
+  protected $entity;
+
   protected static $mapValue = [
     'key1' => 'value',
     'key2' => 'no, val you',
@@ -37,13 +46,24 @@ class EntityTestMapItemNormalizerTest extends EntityTestResourceTestBase {
   /**
    * {@inheritdoc}
    */
-  protected static $mimeType = 'application/json';
+  protected function setUpAuthorization($method) {
+    $this->grantPermissionsToTestedRole(['administer entity_test content']);
+  }
 
   /**
    * {@inheritdoc}
    */
-  protected function setUpAuthorization($method) {
-    $this->grantPermissionsToTestedRole(['administer entity_test content']);
+  protected function createEntity() {
+    $entity = EntityTestMapField::create([
+      'name' => 'Llama',
+      'type' => 'entity_test_map_field',
+      'data' => [
+        0 => static::$mapValue,
+      ]
+    ]);
+    $entity->setOwnerId(0);
+    $entity->save();
+    return $entity;
   }
 
   /**
@@ -82,22 +102,6 @@ protected function getExpectedNormalizedEntity() {
   /**
    * {@inheritdoc}
    */
-  protected function createEntity() {
-    $entity = EntityTestMapField::create([
-      'name' => 'Llama',
-      'type' => 'entity_test_map_field',
-      'data' => [
-        0 => static::$mapValue,
-      ]
-    ]);
-    $entity->setOwnerId(0);
-    $entity->save();
-    return $entity;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   protected function getNormalizedPostEntity() {
     return [
       'name' => [
@@ -122,6 +126,7 @@ protected function getExpectedUnauthorizedAccessMessage($method) {
     return "The 'administer entity_test content' permission is required.";
   }
 
+
   /**
    * {@inheritdoc}
    */