.../Comment/CommentResourceTestBase.php            | 53 ++++++++++++++++------
 .../rest/tests/src/Functional/ResourceTestBase.php |  4 ++
 2 files changed, 42 insertions(+), 15 deletions(-)

diff --git a/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php b/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php
index cb50160..c03d45e 100644
--- a/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/EntityResource/Comment/CommentResourceTestBase.php
@@ -8,6 +8,7 @@
 use Drupal\entity_test\Entity\EntityTest;
 use Drupal\Tests\rest\Functional\EntityResource\EntityResourceTestBase;
 use Drupal\user\Entity\User;
+use GuzzleHttp\RequestOptions;
 
 abstract class CommentResourceTestBase extends EntityResourceTestBase {
 
@@ -41,21 +42,6 @@ protected function setUpAuthorization($method) {
    * {@inheritdoc}
    */
   protected function createEntity() {
-//    // Create a "Camelids" node type.
-//    NodeType::create([
-//      'name' => 'Camelids',
-//      'type' => 'camelids',
-//    ])->save();
-//
-//    // Create a "Llama" node.
-//    $node = Node::create(['type' => 'camelids']);
-//    $node->setTitle('Llama')
-//      ->setPublished(TRUE)
-//      ->setCreatedTime(123456789)
-//      ->setChangedTime(123456789)
-//      ->setRevisionCreationTime(123456789)
-//      ->save();
-
     // Create a "bar" bundle for the "entity_test" entity type and create.
     $bundle = 'bar';
     entity_test_create_bundle($bundle, NULL, 'entity_test');
@@ -221,4 +207,41 @@ protected function getNormalizedEntityToCreate() {
     ];
   }
 
+  public function testPostDxWithoutCriticalBaseFields() {
+    $this->provisionEntityResource();
+    $this->setUpAuthorization('POST');
+
+    $url = $this->getPostUrl()->setOption('query', ['_format' => static::$format]);
+    $request_options = [];
+    $request_options[RequestOptions::HEADERS]['Content-Type'] = static::$mimeType;
+    $request_options = array_merge_recursive($request_options, $this->getAuthenticationRequestOptions());
+
+    // DX: 422 when missing 'entity_type' field.
+    $request_options[RequestOptions::BODY] = $this->serializer->encode(array_diff_key($this->getNormalizedEntityToCreate(), ['entity_type' => TRUE]), static::$format);
+    $response = $this->request('POST', $url, $request_options);
+    // @todo Remove the first line in favor of the commented line in https://www.drupal.org/node/2820364.
+    $this->assertResourceErrorResponse(500, 'A fatal error occurred: Internal Server Error', $response);
+    //$this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nentity_type: This value should not be null.\n", $response);
+
+    // DX: 422 when missing 'entity_id' field.
+    $request_options[RequestOptions::BODY] = $this->serializer->encode(array_diff_key($this->getNormalizedEntityToCreate(), ['entity_id' => TRUE]), static::$format);
+    // @todo Remove the try/catch in favor of the two commented lines in https://www.drupal.org/node/2820364.
+    try {
+      $this->request('POST', $url, $request_options);
+      $this->assertSame(TRUE, FALSE);
+    }
+    catch (\Exception $e) {
+      $this->assertSame("Error: Call to a member function get() on null\nDrupal\\comment\\Plugin\\Validation\\Constraint\\CommentNameConstraintValidator->getAnonymousContactDetailsSetting()() (Line: 96)\n", $e->getMessage());
+    }
+    //$response = $this->request('POST', $url, $request_options);
+    //$this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nentity_type: This value should not be null.\n", $response);
+
+    // DX: 422 when missing 'entity_type' field.
+    $request_options[RequestOptions::BODY] = $this->serializer->encode(array_diff_key($this->getNormalizedEntityToCreate(), ['field_name' => TRUE]), static::$format);
+    $response = $this->request('POST', $url, $request_options);
+    // @todo Remove the first line in favor of the commented line in https://www.drupal.org/node/2820364.
+    $this->assertResourceErrorResponse(500, 'A fatal error occurred: Field  is unknown.', $response);
+    //$this->assertResourceErrorResponse(422, "Unprocessable Entity: validation failed.\nfield_name: This value should not be null.\n", $response);
+  }
+
 }
diff --git a/core/modules/rest/tests/src/Functional/ResourceTestBase.php b/core/modules/rest/tests/src/Functional/ResourceTestBase.php
index 1c212bb..36a4a5a 100644
--- a/core/modules/rest/tests/src/Functional/ResourceTestBase.php
+++ b/core/modules/rest/tests/src/Functional/ResourceTestBase.php
@@ -8,6 +8,7 @@
 use Drupal\user\Entity\Role;
 use Drupal\user\RoleInterface;
 use GuzzleHttp\Exception\ClientException;
+use GuzzleHttp\Exception\ServerException;
 use Psr\Http\Message\ResponseInterface;
 
 /**
@@ -250,6 +251,9 @@ protected function request($method, Url $url, array $request_options) {
     catch (ClientException $e) {
       $response = $e->getResponse();
     }
+    catch (ServerException $e) {
+      $response = $e->getResponse();
+    }
     return $response;
   }