Incomplete message template migration and missing global config migration

1. +++ b/src/Plugin/migrate/process/MessageGlobalSettings.php
   @@ -0,0 +1,42 @@
   +class MessageGlobalSettings extends ProcessPluginBase {
   ...
   +    if ($value['message_purge_enable']) {
   ...
   +    return $value['purge_methods'];
   

   What happens if $value['message_purge_enable'] evaluates as FALSE?

   I think that there won't be any purge_methods then, so this will trigger an error.

2. +++ b/src/Plugin/migrate/process/MessageTemplateSettings.php
   @@ -0,0 +1,45 @@
   +class MessageTemplateSettings extends ProcessPluginBase {
   ...
   +    $value['token options']['token replace'] = 1;
   

   Could you please add a comment about why this should be enabled?

3. +++ b/src/Plugin/migrate/process/MessageTemplateSettings.php
   @@ -0,0 +1,45 @@
   +    if ($value['purge']['enabled']) {
   +      $value['purge_methods']['quota'] = [
   ...
   +    }
   +    unset($value['purge']);
   +    return $value;
   

   If purge isn't enabled, then purge_methods should be an empty array.

4. +++ b/tests/src/Kernel/MessageGlobalSettingsMigrateTest.php
   @@ -0,0 +1,68 @@
   +class MessageGlobalSettingsMigrateTest extends MigrateDrupal7TestBase {
   

   It would be very nice if you have added some test data for message templates and actual messages as well.

5. Preexisting issue: d7_message migration is missing the Content tag, and since message template is its bundle entity, it should depend on d7_message_template.
6. Preexisting issue: d7_message_template migration is missing the Configuration tag.

All that (I think) was needed here, was for this patch to be tested in combination with #3256855-4: Duplicate message texts after migration..

1. The test coverage looks great!

2. +++ b/tests/src/Kernel/MessagesMigrateTest.php
   @@ -0,0 +1,69 @@
   + * @group node_class
   

   🐛 s/node_class/message/

3. +++ b/tests/src/Kernel/MessagesMigrateTest.php
   @@ -0,0 +1,69 @@
   +    $this->assertEquals(2, count($result));
   

   Nit: This can use assertCount($2, result) instead to avoid the manual count() call 🤓

That second one is such a nitpick, that first one can easily be fixed by the maintainer on commit. So: marking this RTBC — awesome work here! D'oh, the tests are failing on 9.3! 😬

1. 1) Drupal\Tests\message\Kernel\MessageGlobalSettingsMigrateTest::testMessageGlobalSettingsMigration
   Failed asserting that two arrays are identical.
   

   I bet this is due to https://www.drupal.org/node/3230199 — i.e. all you need is to re-sort these, if my suspicions is correct.

2. 1) Drupal\Tests\message\Kernel\MessageTemplateMigrateTest::testMessageTemplateMigration
   Failed asserting that two arrays are identical.

   Same suspicion.

3. All other test failures are out-of-scope here and are pre-existing bugs in the module! See #3259735: Add daily test against Drupal 9 core minor.

The 8 failures in #12 (see https://www.drupal.org/pift-ci-job/2302552) are identical to those in #3259735-2: Add daily test against Drupal 9 core minor (see https://www.drupal.org/pift-ci-job/2300844). I manually compared those test results.

That means this is de facto green!

Tests are now passing on the main branch, so it looks like this needs a bit of work to get the new tests passing.