diff --git a/src/TextUI/Command/Commands/ListGroupsCommand.php b/src/TextUI/Command/Commands/ListGroupsCommand.php
index 70804bbac70..3cff3d17c4d 100644
--- a/src/TextUI/Command/Commands/ListGroupsCommand.php
+++ b/src/TextUI/Command/Commands/ListGroupsCommand.php
@@ -70,13 +70,13 @@ public function execute(): Result
         );
 
         foreach ($groups as $group => $numberOfTests) {
-            if (str_starts_with($group, '__phpunit_')) {
+            if (str_starts_with((string) $group, '__phpunit_')) {
                 continue;
             }
 
             $buffer .= sprintf(
                 ' - %s (%d test%s)' . PHP_EOL,
-                $group,
+                (string) $group,
                 $numberOfTests,
                 $numberOfTests > 1 ? 's' : '',
             );
diff --git a/src/TextUI/Command/Commands/ListTestsAsXmlCommand.php b/src/TextUI/Command/Commands/ListTestsAsXmlCommand.php
index bfb095d3883..99fab1be3b6 100644
--- a/src/TextUI/Command/Commands/ListTestsAsXmlCommand.php
+++ b/src/TextUI/Command/Commands/ListTestsAsXmlCommand.php
@@ -108,7 +108,7 @@ public function execute(): Result
 
         foreach ($groups as $groupName => $testIds) {
             $writer->startElement('group');
-            $writer->writeAttribute('name', $groupName);
+            $writer->writeAttribute('name', (string) $groupName);
 
             foreach ($testIds as $testId) {
                 $writer->startElement('test');
diff --git a/tests/end-to-end/_files/listing-tests-and-groups/ExampleTest.php b/tests/end-to-end/_files/listing-tests-and-groups/ExampleTest.php
index 2c3c3c99b84..d4f783d722f 100644
--- a/tests/end-to-end/_files/listing-tests-and-groups/ExampleTest.php
+++ b/tests/end-to-end/_files/listing-tests-and-groups/ExampleTest.php
@@ -25,4 +25,10 @@ public function testTwo(): void
     {
         $this->assertTrue(true);
     }
+
+    #[Group('3')]
+    public function testThree(): void
+    {
+        $this->assertTrue(true);
+    }
 }
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-filter.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-filter.phpt
index 30e88fdee42..89827356532 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-filter.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-filter.phpt
@@ -15,5 +15,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
 
-Available test group:
+Available test groups:
+ - 3 (1 test)
  - two (1 test)
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-group.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-group.phpt
index f3558ee4c63..ee4abaffdbc 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-group.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-groups-exclude-group.phpt
@@ -16,5 +16,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 PHPUnit %s by Sebastian Bergmann and contributors.
 
 Available test groups:
+ - 3 (1 test)
  - default (1 test)
  - two (1 test)
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-groups-include-filter.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-groups-include-filter.phpt
index 30e88fdee42..89827356532 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-groups-include-filter.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-groups-include-filter.phpt
@@ -15,5 +15,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
 
-Available test group:
+Available test groups:
+ - 3 (1 test)
  - two (1 test)
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-groups.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-groups.phpt
index fcb77b4edb3..449f5d365e0 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-groups.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-groups.phpt
@@ -14,6 +14,7 @@ require_once __DIR__ . '/../../../bootstrap.php';
 PHPUnit %s by Sebastian Bergmann and contributors.
 
 Available test groups:
+ - 3 (1 test)
  - default (1 test)
  - one (1 test)
  - two (1 test)
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-filter.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-filter.phpt
index 17b6b8b5d7f..80fcfb60c8e 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-filter.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-filter.phpt
@@ -15,5 +15,6 @@ require_once __DIR__ . '/../../../bootstrap.php';
 --EXPECTF--
 PHPUnit %s by Sebastian Bergmann and contributors.
 
-Available test:
+Available tests:
  - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo
+ - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-group.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-group.phpt
index 825ccf63c6b..0d0eccd8447 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-group.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-exclude-group.phpt
@@ -17,4 +17,5 @@ PHPUnit %s by Sebastian Bergmann and contributors.
 
 Available tests:
  - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo
+ - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree
  - %sexample.phpt
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-filter.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-filter.phpt
index 8e2b4df05f6..00546a2c6ff 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-filter.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-filter.phpt
@@ -21,9 +21,13 @@ PHPUnit %s by Sebastian Bergmann and contributors.
  <tests>
   <testClass name="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest" file="%sExampleTest.php">
    <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo" name="testTwo"/>
+   <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree" name="testThree"/>
   </testClass>
  </tests>
  <groups>
+  <group name="3">
+   <test id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree"/>
+  </group>
   <group name="two">
    <test id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo"/>
   </group>
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-group.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-group.phpt
index 6357a72a825..9b6dec2cd48 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-group.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml-exclude-group.phpt
@@ -21,10 +21,14 @@ PHPUnit %s by Sebastian Bergmann and contributors.
  <tests>
   <testClass name="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest" file="%sExampleTest.php">
    <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo" name="testTwo"/>
+   <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree" name="testThree"/>
   </testClass>
   <phpt file="%sexample.phpt"/>
  </tests>
  <groups>
+  <group name="3">
+   <test id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree"/>
+  </group>
   <group name="two">
    <test id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo"/>
   </group>
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml.phpt
index ff423cf6f09..2be58670f44 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-tests-xml.phpt
@@ -21,10 +21,14 @@ PHPUnit %s by Sebastian Bergmann and contributors.
   <testClass name="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest" file="%sExampleTest.php">
    <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testOne" name="testOne"/>
    <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo" name="testTwo"/>
+   <testMethod id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree" name="testThree"/>
   </testClass>
   <phpt file="%sexample.phpt"/>
  </tests>
  <groups>
+  <group name="3">
+   <test id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree"/>
+  </group>
   <group name="one">
    <test id="PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testOne"/>
   </group>
diff --git a/tests/end-to-end/cli/listing-tests-and-groups/list-tests.phpt b/tests/end-to-end/cli/listing-tests-and-groups/list-tests.phpt
index 8946bb63b6d..e443b7331bd 100644
--- a/tests/end-to-end/cli/listing-tests-and-groups/list-tests.phpt
+++ b/tests/end-to-end/cli/listing-tests-and-groups/list-tests.phpt
@@ -16,4 +16,5 @@ PHPUnit %s by Sebastian Bergmann and contributors.
 Available tests:
  - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testOne
  - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testTwo
+ - PHPUnit\TestFixture\ListingTestsAndGroups\ExampleTest::testThree
  - %sexample.phpt