diff --git a/core/modules/system/src/Tests/Theme/ThemeSuggestionsAlterTest.php b/core/modules/system/src/Tests/Theme/ThemeSuggestionsAlterTest.php
index a6bfa2a..ced406e 100644
--- a/core/modules/system/src/Tests/Theme/ThemeSuggestionsAlterTest.php
+++ b/core/modules/system/src/Tests/Theme/ThemeSuggestionsAlterTest.php
@@ -152,18 +152,6 @@ public function testSuggestionsAlterInclude() {
   }
 
   /**
-   * Tests hook_theme_suggestions_HOOK() with invalid single suggestions.
-   */
-  public function testInvalidThemeSuggestion() {
-    // An invalid suggestion that has a valid derived suggestion.
-    $this->drupalGet('theme-test/invalid-suggestion-derived');
-    $this->assertText('Template for testing suggestion hooks with an array of theme suggestions.');
-
-    $this->drupalGet('theme-test/invalid-suggestion');
-    $this->assertNoText('Template');
-  }
-
-  /**
    * Tests hook_theme_suggestions_HOOK() with direct array suggestions.
    */
   public function testArraySuggestions() {
diff --git a/core/modules/system/tests/modules/theme_test/src/ThemeTestController.php b/core/modules/system/tests/modules/theme_test/src/ThemeTestController.php
index 5aa5895..522f8de 100644
--- a/core/modules/system/tests/modules/theme_test/src/ThemeTestController.php
+++ b/core/modules/system/tests/modules/theme_test/src/ThemeTestController.php
@@ -162,24 +162,6 @@ public function arraySuggestionsSpecific() {
   }
 
   /**
-   * @TODO
-   */
-  public function invalidSuggestionDerived() {
-    return [
-      '#theme' => 'theme_test_array_suggestions__not_implemented',
-    ];
-  }
-
-  /**
-   * @TODO
-   */
-  public function invalidSuggestion() {
-    return [
-      '#theme' => 'theme_test_array_not_implemented',
-    ];
-  }
-
-  /**
    * Controller to ensure that no theme is initialized.
    *
    * @return \Symfony\Component\HttpFoundation\JsonResponse
diff --git a/core/modules/system/tests/modules/theme_test/theme_test.routing.yml b/core/modules/system/tests/modules/theme_test/theme_test.routing.yml
index 8cf5924..3a79cf6 100644
--- a/core/modules/system/tests/modules/theme_test/theme_test.routing.yml
+++ b/core/modules/system/tests/modules/theme_test/theme_test.routing.yml
@@ -118,20 +118,6 @@ theme_test.array_suggestions_specific:
   requirements:
     _access: 'TRUE'
 
-theme_test.invalid_suggestion:
-  path: '/theme-test/invalid-suggestion'
-  defaults:
-    _controller: '\Drupal\theme_test\ThemeTestController::invalidSuggestion'
-  requirements:
-    _access: 'TRUE'
-
-theme_test.invalid_suggestion_derived:
-  path: '/theme-test/invalid-suggestion-derived'
-  defaults:
-    _controller: '\Drupal\theme_test\ThemeTestController::invalidSuggestionDerived'
-  requirements:
-    _access: 'TRUE'
-
 theme_test.non_html:
   path: '/theme-test/non-html'
   defaults: