diff --git a/core/tests/Drupal/Tests/Core/Asset/AssetResolverTest.php b/core/tests/Drupal/Tests/Core/Asset/AssetResolverTest.php
index f0f3cbf93c1a9d912f354f7ca87c16dedff86b73..f9f58764db8bcf28be9c000c160a0187f94a81f9 100644
--- a/core/tests/Drupal/Tests/Core/Asset/AssetResolverTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/AssetResolverTest.php
@@ -86,9 +86,6 @@ protected function setUp(): void {
     $active_theme = $this->getMockBuilder('\Drupal\Core\Theme\ActiveTheme')
       ->disableOriginalConstructor()
       ->getMock();
-    $active_theme->expects($this->any())
-      ->method('getName')
-      ->willReturn('bartik');
     $this->themeManager->expects($this->any())
       ->method('getActiveTheme')
       ->willReturn($active_theme);
diff --git a/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php b/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php
index 2c7fad24627c45e3890b5df670f87baebac547a5..fb6b0fed24b9be18b57088b7eb98fbb44e72f62b 100644
--- a/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php
+++ b/core/tests/Drupal/Tests/Core/Asset/CssCollectionGrouperUnitTest.php
@@ -81,7 +81,7 @@ public function testGrouper() {
         'type' => 'file',
         'weight' => 0.001,
         'preprocess' => TRUE,
-        'data' => 'core/themes/bartik/css/base/elements.css',
+        'data' => 'core/themes/example/css/base/elements.css',
         'basename' => 'elements.css',
       ],
       'print.css' => [
@@ -90,7 +90,7 @@ public function testGrouper() {
         'type' => 'file',
         'weight' => 0.003,
         'preprocess' => TRUE,
-        'data' => 'core/themes/bartik/css/print.css',
+        'data' => 'core/themes/example/css/print.css',
         'basename' => 'print.css',
       ],
     ];
diff --git a/core/tests/Drupal/Tests/Core/Command/GenerateThemeTest.php b/core/tests/Drupal/Tests/Core/Command/GenerateThemeTest.php
index 792c707e1e209c8b67a08e834b8cecf1830d9a95..9ebc09bdc8cfb42adbd9fcf4f268fadc5c4d6f9c 100644
--- a/core/tests/Drupal/Tests/Core/Command/GenerateThemeTest.php
+++ b/core/tests/Drupal/Tests/Core/Command/GenerateThemeTest.php
@@ -311,12 +311,12 @@ public function testStarterKitFlag(): void {
       '--name="Test custom starterkit theme"',
       '--description="Custom theme generated from a starterkit theme"',
       '--starterkit',
-      'bartik',
+      'olivero',
     ];
     $process = new Process($install_command, NULL);
     $process->setTimeout(60);
     $result = $process->run();
-    $this->assertStringContainsString('Theme source theme bartik is not a valid starter kit.', trim($process->getErrorOutput()));
+    $this->assertStringContainsString('Theme source theme olivero is not a valid starter kit.', trim($process->getErrorOutput()));
     $this->assertSame(1, $result);
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Extension/ExtensionDiscoveryTest.php b/core/tests/Drupal/Tests/Core/Extension/ExtensionDiscoveryTest.php
index 70809aabbec2e449b9098d706beab37c7f8e750a..e70e05c0f51307f4b06982f5ed6c2d3ef7e84d01 100644
--- a/core/tests/Drupal/Tests/Core/Extension/ExtensionDiscoveryTest.php
+++ b/core/tests/Drupal/Tests/Core/Extension/ExtensionDiscoveryTest.php
@@ -141,13 +141,6 @@ protected function populateFilesystemStructure(array &$filesystem_structure) {
       'core/modules/user/user.info.yml' => [],
       'profiles/other_profile/modules/other_profile_nested_module/other_profile_nested_module.info.yml' => [],
       'core/modules/system/system.info.yml' => [],
-      'core/themes/seven/seven.info.yml' => [
-        'type' => 'theme',
-      ],
-      // Override the core instance of the 'seven' theme.
-      'sites/default/themes/seven/seven.info.yml' => [
-        'type' => 'theme',
-      ],
       'modules/devel/devel.info.yml' => [],
       'modules/poorly_placed_theme/poorly_placed_theme.info.yml' => [
         'type' => 'theme',
diff --git a/core/tests/Drupal/Tests/Core/Extension/ThemeHandlerTest.php b/core/tests/Drupal/Tests/Core/Extension/ThemeHandlerTest.php
index fcf69c16bbb0d10e0a05e6ec355c4a6d138eabea..c06d828c84828d6e464fec8d6f064c0352ff66eb 100644
--- a/core/tests/Drupal/Tests/Core/Extension/ThemeHandlerTest.php
+++ b/core/tests/Drupal/Tests/Core/Extension/ThemeHandlerTest.php
@@ -80,18 +80,18 @@ public function testRebuildThemeData() {
     $this->themeList->expects($this->once())
       ->method('getList')
       ->will($this->returnValue([
-        'seven' => new Extension($this->root, 'theme', 'core/themes/seven/seven.info.yml', 'seven.theme'),
+        'stark' => new Extension($this->root, 'theme', 'core/themes/stark/stark.info.yml', 'stark.theme'),
       ]));
 
     $theme_data = $this->themeHandler->rebuildThemeData();
     $this->assertCount(1, $theme_data);
-    $info = $theme_data['seven'];
+    $info = $theme_data['stark'];
 
     // Ensure some basic properties.
     $this->assertInstanceOf('Drupal\Core\Extension\Extension', $info);
-    $this->assertEquals('seven', $info->getName());
-    $this->assertEquals('core/themes/seven/seven.info.yml', $info->getPathname());
-    $this->assertEquals('core/themes/seven/seven.theme', $info->getExtensionPathname());
+    $this->assertEquals('stark', $info->getName());
+    $this->assertEquals('core/themes/stark/stark.info.yml', $info->getPathname());
+    $this->assertEquals('core/themes/stark/stark.theme', $info->getExtensionPathname());
 
   }
 
diff --git a/core/tests/Drupal/Tests/Core/Theme/AjaxBasePageNegotiatorTest.php b/core/tests/Drupal/Tests/Core/Theme/AjaxBasePageNegotiatorTest.php
index ce62788bf423a789d90547162e9b671d154d6349..538b9c33a71961849796e1e5eb59c9f38b3ce6a0 100644
--- a/core/tests/Drupal/Tests/Core/Theme/AjaxBasePageNegotiatorTest.php
+++ b/core/tests/Drupal/Tests/Core/Theme/AjaxBasePageNegotiatorTest.php
@@ -45,7 +45,7 @@ protected function setUp(): void {
     parent::setUp();
 
     $this->tokenGenerator = $this->prophesize(CsrfTokenGenerator::class);
-    $config_factory = $this->getConfigFactoryStub(['system.theme' => ['default' => 'bartik']]);
+    $config_factory = $this->getConfigFactoryStub(['system.theme' => ['default' => 'stark']]);
     $this->requestStack = new RequestStack();
     $this->negotiator = new AjaxBasePageNegotiator($this->tokenGenerator->reveal(), $config_factory, $this->requestStack);
   }
@@ -68,8 +68,8 @@ public function providerTestApplies() {
     $data = [];
     $data['empty'] = [[], FALSE];
     $data['no_theme'] = [['ajax_page_state' => ['theme' => '', 'theme_token' => '']], FALSE];
-    $data['valid_theme_empty_theme_token'] = [['ajax_page_state' => ['theme' => 'seven', 'theme_token' => '']], TRUE];
-    $data['valid_theme_valid_theme_token'] = [['ajax_page_state' => ['theme' => 'seven', 'theme_token' => 'valid_theme_token']], TRUE];
+    $data['valid_theme_empty_theme_token'] = [['ajax_page_state' => ['theme' => 'claro', 'theme_token' => '']], TRUE];
+    $data['valid_theme_valid_theme_token'] = [['ajax_page_state' => ['theme' => 'claro', 'theme_token' => 'valid_theme_token']], TRUE];
     return $data;
   }
 
@@ -77,7 +77,7 @@ public function providerTestApplies() {
    * @covers ::determineActiveTheme
    */
   public function testDetermineActiveThemeValidToken() {
-    $theme = 'seven';
+    $theme = 'claro';
     $theme_token = 'valid_theme_token';
 
     $request = new Request([], ['ajax_page_state' => ['theme' => $theme, 'theme_token' => $theme_token]]);
@@ -95,7 +95,7 @@ public function testDetermineActiveThemeValidToken() {
    * @covers ::determineActiveTheme
    */
   public function testDetermineActiveThemeInvalidToken() {
-    $theme = 'seven';
+    $theme = 'claro';
     $theme_token = 'invalid_theme_token';
 
     $request = new Request([], ['ajax_page_state' => ['theme' => $theme, 'theme_token' => $theme_token]]);
@@ -113,7 +113,7 @@ public function testDetermineActiveThemeInvalidToken() {
    * @covers ::determineActiveTheme
    */
   public function testDetermineActiveThemeDefaultTheme() {
-    $theme = 'bartik';
+    $theme = 'stark';
     // When the theme is the system default, an empty string is provided as the
     // theme token. See system_js_settings_alter().
     $theme_token = '';