diff --git a/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php b/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php
index 422eb0b..9df801e 100644
--- a/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/LibraryDiscoveryParserTest.php
@@ -503,60 +503,49 @@ public function testLibraryWithLicenses() {
   }
 
   /**
-   * Verify an assertion fails if CSS declarations have non-existent categories.
+   * Verifies assertions catch invalid CSS declarations.
+   *
+   * @dataProvider providerTestCssAssert
    */
-  public function testCssCategoryAssert() {
-    $this->moduleHandler->expects($this->atLeastOnce())
-      ->method('moduleExists')
-      ->with('css_bad_category')
-      ->will($this->returnValue(TRUE));
-
-    $path = __DIR__ . '/library_test_files';
-    $path = substr($path, strlen($this->root) + 1);
-    $this->libraryDiscoveryParser->setPaths('module', 'css_bad_category', $path);
-
-    // This will fail since the CSS declaration isn't properly nested under
-    // a category.
-    $this->setExpectedException(\AssertionError::class, 'Invalid CSS category: bad_category. See https://www.drupal.org/node/2274843.');
-    $this->libraryDiscoveryParser->buildByExtension('css_bad_category');
-  }
 
   /**
-   * Verify an assertion fails if CSS declarations aren't properly nested.
+   * Verify an assertion fails if CSS declarations have non-existent categories.
+   *
+   * @param string $extension
+   *   The css extension to build.
+   * @param string $exception_message
+   *   The expected exception message.
+   *
+   * @dataProvider providerTestCssAssert
    */
-  public function testCssNestingAssert() {
+  public function testCssAssert($extension, $exception_message) {
     $this->moduleHandler->expects($this->atLeastOnce())
       ->method('moduleExists')
-      ->with('css_bad_nesting')
+      ->with($extension)
       ->will($this->returnValue(TRUE));
 
     $path = __DIR__ . '/library_test_files';
     $path = substr($path, strlen($this->root) + 1);
-    $this->libraryDiscoveryParser->setPaths('module', 'css_bad_nesting', $path);
+    $this->libraryDiscoveryParser->setPaths('module', $extension, $path);
 
-    // This will fail since the CSS declaration isn't properly nested under
-    // a category.
-    $this->setExpectedException(\AssertionError::class, 'CSS must be nested under a category. See https://www.drupal.org/node/2274843.');
-    $this->libraryDiscoveryParser->buildByExtension('css_bad_nesting');
+    $this->setExpectedException(\AssertionError::class, $exception_message);
+    $this->libraryDiscoveryParser->buildByExtension($extension);
   }
 
   /**
-   * Verify an assertion fails if CSS declarations are a simple array of files.
+   * Data provider for testing bad CSS declarations.
    */
-  public function testCssNestingArrayAssert() {
-    $this->moduleHandler->expects($this->atLeastOnce())
-      ->method('moduleExists')
-      ->with('css_bad_nesting_array')
-      ->will($this->returnValue(TRUE));
+  public function providerTestCssAssert() {
+    return [
+      // Invalid category.
+      ['css_bad_category', 'Invalid CSS category: bad_category. See https://www.drupal.org/node/2274843.'] ,
 
-    $path = __DIR__ . '/library_test_files';
-    $path = substr($path, strlen($this->root) + 1);
-    $this->libraryDiscoveryParser->setPaths('module', 'css_bad_nesting_array', $path);
+      // Improper CSS nesting.
+      ['css_bad_nesting', 'CSS must be nested under a category. See https://www.drupal.org/node/2274843.'],
 
-    // This will fail since the CSS declaration isn't properly nested under
-    // a category.
-    $this->setExpectedException(\AssertionError::class, 'CSS files should be specified as key/value pairs, where the values are configuration options. See https://www.drupal.org/node/2274843.');
-    $this->libraryDiscoveryParser->buildByExtension('css_bad_nesting_array');
+      // Improper nesting with bad key value pairs.
+      ['css_bad_nesting_array', 'CSS files should be specified as key/value pairs, where the values are configuration options. See https://www.drupal.org/node/2274843.'],
+    ];
   }
 
 }
diff --git a/core/tests/Drupal/Tests/Core/Asset/library_test_files/css_bad_nesting_array.libraries.yml b/core/tests/Drupal/Tests/Core/Asset/library_test_files/css_bad_nesting_array.libraries.yml
index db028d9..3c59bc7 100644
--- a/core/tests/Drupal/Tests/Core/Asset/library_test_files/css_bad_nesting_array.libraries.yml
+++ b/core/tests/Drupal/Tests/Core/Asset/library_test_files/css_bad_nesting_array.libraries.yml
@@ -1,4 +1,4 @@
 bad_nesting_array:
   css:
-    # Specified as an array will break. 
+    # Specified as an array will break.
     - css/styles.css
diff --git a/core/tests/Drupal/Tests/Core/Asset/library_test_files/dependencies.libraries.yml b/core/tests/Drupal/Tests/Core/Asset/library_test_files/dependencies.libraries.yml
index 068a9a3..169d2f4 100644
--- a/core/tests/Drupal/Tests/Core/Asset/library_test_files/dependencies.libraries.yml
+++ b/core/tests/Drupal/Tests/Core/Asset/library_test_files/dependencies.libraries.yml
@@ -1,7 +1,7 @@
 example:
   css:
     theme:
-      css/example.js: {}
+      css/example.css: {}
   dependencies:
     - external/example_external
     - example_module/example