RouteNotFoundException: Route "jsonapi.[entity].[field_name].related" does not exist

Thanks for the issue and patch. If this is still relevant, it needs a reroll for 9.2.

Rerolled the patch in #2, thanks!

The patch looks good and applies cleanly on 9.2.x-dev.
Looks good to be merged.

This needs some test coverage.

Updating tags.

@mohit_aghera asked for pointers on wrtitng a test for this issue in #bugsmash. Just sharing the relevant information here.

We can write a same test as \Drupal\Tests\jsonapi\Kernel\Normalizer\JsonApiDocumentTopLevelNormalizerTest::testNormalizeException() to test this.

Adding test cases and test-only patch.

Trying to fix the test cases. Updated cardinality.
Even with cardinality 1 it was passing on local somehow. Let's see how it goes.

Please do not ask the testbot to try again until #3207086: [HEAD BROKEN] Consistent failure in MonthDatePluginTest is fixed.

#3207086: [HEAD BROKEN] Consistent failure in MonthDatePluginTest is fixed. I have not reviewed the code.

Committed and pushed d84f620c57 to 9.2.x and 282d000ec5 to 9.1.x. Thanks!

diff --git a/core/modules/jsonapi/tests/src/Kernel/Normalizer/JsonApiDocumentTopLevelNormalizerTest.php b/core/modules/jsonapi/tests/src/Kernel/Normalizer/JsonApiDocumentTopLevelNormalizerTest.php
index 63f9df98c2..14e73c44fd 100644
--- a/core/modules/jsonapi/tests/src/Kernel/Normalizer/JsonApiDocumentTopLevelNormalizerTest.php
+++ b/core/modules/jsonapi/tests/src/Kernel/Normalizer/JsonApiDocumentTopLevelNormalizerTest.php
@@ -423,8 +423,8 @@ public function testNormalizeException() {
    * field values for Label only resource.
    */
   public function testAliasFieldRouteException() {
-    $this->assertSame($this->resourceTypeRepository->getByTypeName('node--article')->getPublicName('uid'), 'uid');
-    $this->assertSame($this->resourceTypeRepository->getByTypeName('user--user')->getPublicName('roles'), 'roles');
+    $this->assertSame('uid', $this->resourceTypeRepository->getByTypeName('node--article')->getPublicName('uid'));
+    $this->assertSame('roles', $this->resourceTypeRepository->getByTypeName('user--user')->getPublicName('roles'));
     $resource_type_field_aliases = [
       'node--article' => [
         'uid' => 'author',
@@ -435,8 +435,8 @@ public function testAliasFieldRouteException() {
     ];
     \Drupal::state()->set('jsonapi_test_resource_type_builder.resource_type_field_aliases', $resource_type_field_aliases);
     Cache::invalidateTags(['jsonapi_resource_types']);
-    $this->assertSame($this->resourceTypeRepository->getByTypeName('node--article')->getPublicName('uid'), 'author');
-    $this->assertSame($this->resourceTypeRepository->getByTypeName('user--user')->getPublicName('roles'), 'user_roles');
+    $this->assertSame('author', $this->resourceTypeRepository->getByTypeName('node--article')->getPublicName('uid'));
+    $this->assertSame('user_roles', $this->resourceTypeRepository->getByTypeName('user--user')->getPublicName('roles'));
 
     // Create the request to fetch the articles and fetch included user.
     list($request, $resource_type) = $this->generateProphecies('node', 'article');

The signature is public static function assertSame($expected, $actual, string $message = ''): void - for the message to make sense the expected value needs to come first. Fixed on commit.