diff --git a/core/modules/system/src/Tests/Theme/ThemeInfoTest.php b/core/modules/system/src/Tests/Theme/ThemeInfoTest.php
index 3b1361d..aa069c5 100644
--- a/core/modules/system/src/Tests/Theme/ThemeInfoTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeInfoTest.php
@@ -86,6 +86,10 @@ function testStylesheets() {
     $this->assertIdentical(0, count($this->xpath("//link[contains(@href, 'sub-remove.css')]")), "sub-remove.css not found");
     $this->assertIdentical(0, count($this->xpath("//link[contains(@href, 'base-add.sub-remove.css')]")), "base-add.sub-remove.css not found");
     $this->assertIdentical(0, count($this->xpath("//link[contains(@href, 'base-override.sub-remove.css')]")), "base-override.sub-remove.css not found");
+
+    // Verify that CSS files with the same name are loaded from both the base theme and subtheme.
+    $this->assertIdentical(1, count($this->xpath("//link[contains(@href, '$base/samename.css')]")), "$base/samename.css found");
+    $this->assertIdentical(1, count($this->xpath("//link[contains(@href, '$sub/samename.css')]")), "$sub/samename.css found");
   }
 
   /**
diff --git a/core/modules/system/src/Tests/Theme/ThemeTest.php b/core/modules/system/src/Tests/Theme/ThemeTest.php
index 6737423..0cd4e4e 100644
--- a/core/modules/system/src/Tests/Theme/ThemeTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeTest.php
@@ -181,28 +181,6 @@ function testCSSOverride() {
   }
 
   /**
-   * Ensures that test theme loads an CSS file named same as in parent theme. It
-   * should load both files.
-   *
-   * @see test_theme.info.yml
-   * @see test_theme.libraries.yml
-   */
-  function testCSSWithSameNameAsInParent() {
-    // Take off css preprocessing
-    $config = $this->config('system.performance');
-    $config->set('css.preprocess', 0);
-    $config->save();
-
-    // Reuse the same page as in testPreprocessForSuggestions(). Request page
-    // and ensure that parent and test theme's same named CSS file gets loaded.
-    $this->drupalGet('theme-test/suggestion');
-    $classy_layout_css_url = drupal_get_path('theme', 'classy') .'/css/layout.css';
-    $theme_test_layout_css_url = drupal_get_path('theme', 'test_theme') .'/css/layout.css';
-    $this->assertIdentical(1, count($this->xpath("//link[contains(@href, '" . $classy_layout_css_url . "')]")), $classy_layout_css_url . " found");
-    $this->assertIdentical(1, count($this->xpath("//link[contains(@href, '" . $theme_test_layout_css_url . "')]")), $theme_test_layout_css_url . " found");
-  }
-
-  /**
    * Ensures a themes template is overrideable based on the 'template' filename.
    */
   function testTemplateOverride() {
diff --git a/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml b/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml
index 1c72d30..49e4ba1 100644
--- a/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml
+++ b/core/modules/system/tests/themes/test_basetheme/test_basetheme.libraries.yml
@@ -5,3 +5,4 @@ global-styling:
       base-add.css: {}
       base-add.sub-override.css: {}
       base-add.sub-remove.css: {}
+      samename.css: {}
diff --git a/core/modules/system/tests/themes/test_subtheme/test_subtheme.libraries.yml b/core/modules/system/tests/themes/test_subtheme/test_subtheme.libraries.yml
index efce7ae..931dffe 100644
--- a/core/modules/system/tests/themes/test_subtheme/test_subtheme.libraries.yml
+++ b/core/modules/system/tests/themes/test_subtheme/test_subtheme.libraries.yml
@@ -3,3 +3,4 @@ global-styling:
   css:
     base:
       css/sub-add.css: {}
+      css/samename.css: {}
diff --git a/core/modules/system/tests/themes/test_theme/css/layout.css b/core/modules/system/tests/themes/test_theme/css/layout.css
deleted file mode 100644
index db5765f..0000000
--- a/core/modules/system/tests/themes/test_theme/css/layout.css
+++ /dev/null
@@ -1,7 +0,0 @@
-
-/**
- * This file is for testing CSS file named same as in parent theme through
- * *.libraries.yml file.
- * Used in
- * No contents are necessary.
- */
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 5000e74..9eebc90 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
@@ -14,8 +14,6 @@ description: 'Theme for testing the theme system'
 version: VERSION
 base theme: classy
 core: 8.x
-libraries:
-  - test_theme/global-styling
 stylesheets-remove:
   - system.module.css
 regions:
diff --git a/core/modules/system/tests/themes/test_theme/test_theme.libraries.yml b/core/modules/system/tests/themes/test_theme/test_theme.libraries.yml
deleted file mode 100644
index ed21a2d..0000000
--- a/core/modules/system/tests/themes/test_theme/test_theme.libraries.yml
+++ /dev/null
@@ -1,5 +0,0 @@
-global-styling:
-  version: VERSION
-  css:
-    theme:
-      css/layout.css: {}