drupal_set_message repeat parameter does not work

Just tagging it.

Yup
Here is a patch.
Figuring out where test for this function should be located.

added tests

Uploading tests only . Should fail.

nice
#4 contains fix and tests. Needs review

#4 looks good

I'd prefer to see here a DrupalSetMessageTest converted to KernelTestBase

+++ b/core/modules/system/tests/modules/system_test/src/Controller/SystemTestController.php
@@ -65,6 +65,13 @@ public function drupalSetMessageTest() {
+    drupal_set_message('Non Duplicated message', 'status', FALSE);
+    drupal_set_message('Non Duplicated message', 'status', FALSE);
...
+    drupal_set_message('Duplicated message', 'status', TRUE);
+    drupal_set_message('Duplicated message', 'status', TRUE);

integration tests already all over core within UI (form) tests

+++ b/core/includes/bootstrap.inc
@@ -703,12 +703,14 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
+    unset($new);

I don't see how this unset is necessary. The important change is from $message to $new in the !in_array check.

+++ b/core/includes/bootstrap.inc
@@ -703,12 +703,14 @@ function drupal_set_message($message = NULL, $type = 'status', $repeat = FALSE)
+    unset($new);

Yep this is unnecessary

I'd prefer to see here a DrupalSetMessageTest converted to KernelTestBase

Let's not mix bug fixing with code refactoring. If it is necessary - do that in follow-up

Here is a new patch.
Removed unset.

removed tag

This issue is a normal bug fix, and doesn't include any disruptive changes, so it is allowed per https://www.drupal.org/core/beta-changes. Committed 7473eaf and pushed to 8.0.x. Thanks!