diff --git a/core/modules/system/src/Tests/Ajax/FrameworkTest.php b/core/modules/system/src/Tests/Ajax/FrameworkTest.php
index 6ab1c5e84b9cdd18e3354acf5a958f31135afeea..e3af6b2d40e7e613a05f54e67e7c2f6c15e1f2da 100644
--- a/core/modules/system/src/Tests/Ajax/FrameworkTest.php
+++ b/core/modules/system/src/Tests/Ajax/FrameworkTest.php
@@ -198,7 +198,7 @@ public function testCurrentPathChange() {
    * Tests that overridden CSS files are not added during lazy load.
    */
   public function testLazyLoadOverriddenCSS() {
-    // The test theme overrides system.module.css without an implementation,
+    // The test theme overrides js.module.css without an implementation,
     // thereby removing it.
     \Drupal::service('theme_handler')->install(array('test_theme'));
     $this->config('system.theme')
@@ -214,6 +214,6 @@ public function testLazyLoadOverriddenCSS() {
     // information about the file; we only really care about whether it appears
     // in a LINK or STYLE tag, for which Drupal always adds a query string for
     // cache control.
-    $this->assertNoText('system.module.css?', 'Ajax lazy loading does not add overridden CSS files.');
+    $this->assertNoText('js.module.css?', 'Ajax lazy loading does not add overridden CSS files.');
   }
 }
diff --git a/core/modules/system/src/Tests/Theme/ThemeTest.php b/core/modules/system/src/Tests/Theme/ThemeTest.php
index a84ef8fec01325661a1f927703489d2fd03695d0..3d8b784a86574c99327c1e1b51e6dfea68b971cb 100644
--- a/core/modules/system/src/Tests/Theme/ThemeTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeTest.php
@@ -175,7 +175,7 @@ function testCSSOverride() {
     $config->set('css.preprocess', 0);
     $config->save();
     $this->drupalGet('theme-test/suggestion');
-    $this->assertNoText('system.module.css', "The theme's .info.yml file is able to remove a module CSS file from being added to the page.");
+    $this->assertNoText('js.module.css', 'The theme\'s .info.yml file is able to override a module CSS file from being added to the page.');
 
     // Also test with aggregation enabled, simply ensuring no PHP errors are
     // triggered during drupal_build_css_cache() when a source file doesn't
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.info.yml b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
index fca49c240d02e6dcdd5329398b988aa393052f1f..1c9745f1c364e5a2c030865ab9b59bdc2d70ae28 100644
--- a/core/modules/system/tests/themes/test_theme/test_theme.info.yml
+++ b/core/modules/system/tests/themes/test_theme/test_theme.info.yml
@@ -15,7 +15,7 @@ version: VERSION
 base theme: classy
 core: 8.x
 stylesheets-remove:
-  - '@system/css/system.module.css'
+  - '@system/css/js.module.css'
 libraries:
   - test_theme/global-styling
 libraries-override:
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php
index 209aa64fd61c72dc0a600d6ffcb8b76b7028e96d..8147360f25712059d2d713b6a8037450e28c96ac 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php
@@ -46,15 +46,15 @@ function testGrouper() {
         'browsers' => array('IE' => TRUE, '!IE' => TRUE),
         'basename' => 'system.base.css',
       ),
-      'system.theme.css' => array(
+      'js.module.css' => array(
         'group' => -100,
         'type' => 'file',
         'weight' => 0.013,
         'media' => 'all',
         'preprocess' => TRUE,
-        'data' => 'core/modules/system/system.theme.css',
+        'data' => 'core/modules/system/js.module.css',
         'browsers' => array('IE' => TRUE, '!IE' => TRUE),
-        'basename' => 'system.theme.css',
+        'basename' => 'js.module.css',
       ),
       'jquery.ui.core.css' => array(
         'group' => -100,
@@ -120,7 +120,7 @@ function testGrouper() {
     $this->assertSame($group['preprocess'], TRUE);
     $this->assertSame(count($group['items']), 3);
     $this->assertContains($css_assets['system.base.css'], $group['items']);
-    $this->assertContains($css_assets['system.theme.css'], $group['items']);
+    $this->assertContains($css_assets['js.module.css'], $group['items']);
 
     // Check group 2.
     $group = $groups[1];