diff --git a/core/modules/jsonapi/tests/src/Functional/CommentExtrasTest.php b/core/modules/jsonapi/tests/src/Functional/CommentExtrasTest.php
new file mode 100644
index 0000000000000000000000000000000000000000..4de862de7fc5fc9bc80b2df56625c28d0ffbcb15
--- /dev/null
+++ b/core/modules/jsonapi/tests/src/Functional/CommentExtrasTest.php
@@ -0,0 +1,112 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\jsonapi\Functional;
+
+use Drupal\Core\Url;
+use Drupal\Component\Utility\NestedArray;
+use Drupal\Component\Serialization\Json;
+use GuzzleHttp\RequestOptions;
+
+/**
+ * JSON:API integration test for the "Comment" content entity type.
+ *
+ * @group jsonapi
+ */
+class CommentExtrasTest extends CommentTest {
+
+  public function setUp(): void {
+    // Don't run any test methods from CommentTest because those will get run
+    // for CommentTest itself.
+    if (method_exists(parent::class, $this->name())) {
+      $this->markTestSkipped();
+    }
+    parent::setUp();
+  }
+
+  /**
+   * Tests POSTing a comment without critical base fields.
+   *
+   * Note that testPostIndividual() is testing with the most minimal
+   * normalization possible: the one returned by ::getNormalizedPostEntity().
+   *
+   * But Comment entities have some very special edge cases:
+   * - base fields that are not marked as required in
+   *   \Drupal\comment\Entity\Comment::baseFieldDefinitions() yet in fact are
+   *   required.
+   * - base fields that are marked as required, but yet can still result in
+   *   validation errors other than "missing required field".
+   */
+  public function testPostIndividualDxWithoutCriticalBaseFields(): void {
+    $this->setUpAuthorization('POST');
+    $this->config('jsonapi.settings')->set('read_only', FALSE)->save(TRUE);
+
+    $url = Url::fromRoute(sprintf('jsonapi.%s.collection.post', static::$resourceTypeName));
+    $request_options = [];
+    $request_options[RequestOptions::HEADERS]['Accept'] = 'application/vnd.api+json';
+    $request_options[RequestOptions::HEADERS]['Content-Type'] = 'application/vnd.api+json';
+    $request_options = NestedArray::mergeDeep($request_options, $this->getAuthenticationRequestOptions());
+
+    $remove_field = function (array $normalization, $type, $attribute_name) {
+      unset($normalization['data'][$type][$attribute_name]);
+      return $normalization;
+    };
+
+    // DX: 422 when missing 'entity_type' field.
+    $request_options[RequestOptions::BODY] = Json::encode($remove_field($this->getPostDocument(), 'attributes', 'entity_type'));
+    $response = $this->request('POST', $url, $request_options);
+    $this->assertResourceErrorResponse(422, 'entity_type: This value should not be null.', NULL, $response, '/data/attributes/entity_type');
+
+    // DX: 422 when missing 'entity_id' field.
+    $request_options[RequestOptions::BODY] = Json::encode($remove_field($this->getPostDocument(), 'relationships', 'entity_id'));
+    // @todo Remove the try/catch in https://www.drupal.org/node/2820364.
+    try {
+      $response = $this->request('POST', $url, $request_options);
+      $this->assertResourceErrorResponse(422, 'entity_id: This value should not be null.', NULL, $response, '/data/attributes/entity_id');
+    }
+    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());
+    }
+
+    // DX: 422 when missing 'field_name' field.
+    $request_options[RequestOptions::BODY] = Json::encode($remove_field($this->getPostDocument(), 'attributes', 'field_name'));
+    $response = $this->request('POST', $url, $request_options);
+    $this->assertResourceErrorResponse(422, 'field_name: This value should not be null.', NULL, $response, '/data/attributes/field_name');
+  }
+
+  /**
+   * Tests POSTing a comment with and without 'skip comment approval'.
+   */
+  public function testPostIndividualSkipCommentApproval(): void {
+    $this->setUpAuthorization('POST');
+    $this->config('jsonapi.settings')->set('read_only', FALSE)->save(TRUE);
+
+    // Create request.
+    $request_options = [];
+    $request_options[RequestOptions::HEADERS]['Accept'] = 'application/vnd.api+json';
+    $request_options[RequestOptions::HEADERS]['Content-Type'] = 'application/vnd.api+json';
+    $request_options = NestedArray::mergeDeep($request_options, $this->getAuthenticationRequestOptions());
+    $request_options[RequestOptions::BODY] = Json::encode($this->getPostDocument());
+
+    $url = Url::fromRoute('jsonapi.comment--comment.collection.post');
+
+    // Status should be FALSE when posting as anonymous.
+    $response = $this->request('POST', $url, $request_options);
+    $document = $this->getDocumentFromResponse($response);
+    $this->assertResourceResponse(201, FALSE, $response);
+    $this->assertFalse($document['data']['attributes']['status']);
+    $this->assertFalse($this->entityStorage->loadUnchanged(2)->isPublished());
+
+    // Grant anonymous permission to skip comment approval.
+    $this->grantPermissionsToTestedRole(['skip comment approval']);
+
+    // Status must be TRUE when posting as anonymous and skip comment approval.
+    $response = $this->request('POST', $url, $request_options);
+    $document = $this->getDocumentFromResponse($response);
+    $this->assertResourceResponse(201, FALSE, $response);
+    $this->assertTrue($document['data']['attributes']['status']);
+    $this->assertTrue($this->entityStorage->loadUnchanged(3)->isPublished());
+  }
+
+}
diff --git a/core/modules/jsonapi/tests/src/Functional/CommentTest.php b/core/modules/jsonapi/tests/src/Functional/CommentTest.php
index da7d6a7d82247a4a9a46cc57f7fe6be5557afd8d..28660453180e6f7ca6614358bacbbbd95ef63f7d 100644
--- a/core/modules/jsonapi/tests/src/Functional/CommentTest.php
+++ b/core/modules/jsonapi/tests/src/Functional/CommentTest.php
@@ -8,7 +8,6 @@
 use Drupal\comment\Entity\CommentType;
 use Drupal\comment\Plugin\Field\FieldType\CommentItemInterface;
 use Drupal\comment\Tests\CommentTestTrait;
-use Drupal\Component\Serialization\Json;
 use Drupal\Component\Utility\NestedArray;
 use Drupal\Core\Cache\Cache;
 use Drupal\Core\Entity\EntityInterface;
@@ -309,90 +308,6 @@ protected function getExpectedUnauthorizedAccessMessage($method) {
     }
   }
 
-  /**
-   * Tests POSTing a comment without critical base fields.
-   *
-   * Note that testPostIndividual() is testing with the most minimal
-   * normalization possible: the one returned by ::getNormalizedPostEntity().
-   *
-   * But Comment entities have some very special edge cases:
-   * - base fields that are not marked as required in
-   *   \Drupal\comment\Entity\Comment::baseFieldDefinitions() yet in fact are
-   *   required.
-   * - base fields that are marked as required, but yet can still result in
-   *   validation errors other than "missing required field".
-   */
-  public function testPostIndividualDxWithoutCriticalBaseFields(): void {
-    $this->setUpAuthorization('POST');
-    $this->config('jsonapi.settings')->set('read_only', FALSE)->save(TRUE);
-
-    $url = Url::fromRoute(sprintf('jsonapi.%s.collection.post', static::$resourceTypeName));
-    $request_options = [];
-    $request_options[RequestOptions::HEADERS]['Accept'] = 'application/vnd.api+json';
-    $request_options[RequestOptions::HEADERS]['Content-Type'] = 'application/vnd.api+json';
-    $request_options = NestedArray::mergeDeep($request_options, $this->getAuthenticationRequestOptions());
-
-    $remove_field = function (array $normalization, $type, $attribute_name) {
-      unset($normalization['data'][$type][$attribute_name]);
-      return $normalization;
-    };
-
-    // DX: 422 when missing 'entity_type' field.
-    $request_options[RequestOptions::BODY] = Json::encode($remove_field($this->getPostDocument(), 'attributes', 'entity_type'));
-    $response = $this->request('POST', $url, $request_options);
-    $this->assertResourceErrorResponse(422, 'entity_type: This value should not be null.', NULL, $response, '/data/attributes/entity_type');
-
-    // DX: 422 when missing 'entity_id' field.
-    $request_options[RequestOptions::BODY] = Json::encode($remove_field($this->getPostDocument(), 'relationships', 'entity_id'));
-    // @todo Remove the try/catch in https://www.drupal.org/node/2820364.
-    try {
-      $response = $this->request('POST', $url, $request_options);
-      $this->assertResourceErrorResponse(422, 'entity_id: This value should not be null.', NULL, $response, '/data/attributes/entity_id');
-    }
-    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());
-    }
-
-    // DX: 422 when missing 'field_name' field.
-    $request_options[RequestOptions::BODY] = Json::encode($remove_field($this->getPostDocument(), 'attributes', 'field_name'));
-    $response = $this->request('POST', $url, $request_options);
-    $this->assertResourceErrorResponse(422, 'field_name: This value should not be null.', NULL, $response, '/data/attributes/field_name');
-  }
-
-  /**
-   * Tests POSTing a comment with and without 'skip comment approval'.
-   */
-  public function testPostIndividualSkipCommentApproval(): void {
-    $this->setUpAuthorization('POST');
-    $this->config('jsonapi.settings')->set('read_only', FALSE)->save(TRUE);
-
-    // Create request.
-    $request_options = [];
-    $request_options[RequestOptions::HEADERS]['Accept'] = 'application/vnd.api+json';
-    $request_options[RequestOptions::HEADERS]['Content-Type'] = 'application/vnd.api+json';
-    $request_options = NestedArray::mergeDeep($request_options, $this->getAuthenticationRequestOptions());
-    $request_options[RequestOptions::BODY] = Json::encode($this->getPostDocument());
-
-    $url = Url::fromRoute('jsonapi.comment--comment.collection.post');
-
-    // Status should be FALSE when posting as anonymous.
-    $response = $this->request('POST', $url, $request_options);
-    $document = $this->getDocumentFromResponse($response);
-    $this->assertResourceResponse(201, FALSE, $response);
-    $this->assertFalse($document['data']['attributes']['status']);
-    $this->assertFalse($this->entityStorage->loadUnchanged(2)->isPublished());
-
-    // Grant anonymous permission to skip comment approval.
-    $this->grantPermissionsToTestedRole(['skip comment approval']);
-
-    // Status must be TRUE when posting as anonymous and skip comment approval.
-    $response = $this->request('POST', $url, $request_options);
-    $document = $this->getDocumentFromResponse($response);
-    $this->assertResourceResponse(201, FALSE, $response);
-    $this->assertTrue($document['data']['attributes']['status']);
-    $this->assertTrue($this->entityStorage->loadUnchanged(3)->isPublished());
-  }
-
   /**
    * {@inheritdoc}
    */