diff --git a/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php b/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php
index a020ab4303..10c745adda 100644
--- a/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php
+++ b/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInBlockFormTest.php
@@ -159,7 +159,7 @@ public function providerTestBlocks() {
     $blocks = [];
     foreach ($this->getTestThemes() as $theme) {
       $blocks += [
-        "$theme--powered" => [
+        "$theme: block-powered" => [
           'theme' => $theme,
           'block_plugin' => 'system_powered_by_block',
           'new_page_text' => 'Can you imagine anyone showing the label on this block',
@@ -168,7 +168,7 @@ public function providerTestBlocks() {
           'button_text' => 'Save Powered by Drupal',
           'toolbar_item' => '#toolbar-item-user',
         ],
-        "$theme--branding" => [
+        "$theme: block-branding" => [
           'theme' => $theme,
           'block_plugin' => 'system_branding_block',
           'new_page_text' => 'The site that will live a very short life',
@@ -177,7 +177,7 @@ public function providerTestBlocks() {
           'button_text' => 'Save Site branding',
           'toolbar_item' => '#toolbar-item-administration',
         ],
-        "$theme--search" => [
+        "$theme: block-search" => [
           'theme' => $theme,
           'block_plugin' => 'search_form_block',
           'new_page_text' => NULL,
@@ -188,7 +188,7 @@ public function providerTestBlocks() {
         ],
         // This is the functional JS test coverage accompanying
         // \Drupal\Tests\outside_in\Functional\OutsideInTest::testPossibleAnnotations().
-        "$theme--" . OffCanvasFormAnnotationIsClassBlock::class => [
+        "$theme: " . OffCanvasFormAnnotationIsClassBlock::class => [
           'theme' => $theme,
           'block_plugin' => 'outside_in_test_class',
           'new_page_text' => NULL,
@@ -199,7 +199,7 @@ public function providerTestBlocks() {
         ],
         // This is the functional JS test coverage accompanying
         // \Drupal\Tests\outside_in\Functional\OutsideInTest::testPossibleAnnotations().
-        "$theme--" . OffCanvasFormAnnotationNoneBlock::class => [
+        "$theme: " . OffCanvasFormAnnotationNoneBlock::class => [
           'theme' => $theme,
           'block_plugin' => 'outside_in_test_none',
           'new_page_text' => NULL,