diff -u b/core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php b/core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php
--- b/core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php
+++ b/core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php
@@ -20,8 +20,8 @@
 
     // The full path is returned therefore only tests with
     // assertStringEndsWith() so the test is portable.
-    $path = str_replace('/', DIRECTORY_SEPARATOR, 'core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php');
-    $this->assertStringEndsWith($path, $finder->findFile(ClassFinderTest::class));
+    $expected_path = str_replace('/', DIRECTORY_SEPARATOR, 'core/tests/Drupal/Tests/Component/ClassFinder/ClassFinderTest.php');
+    $this->assertStringEndsWith($expected_path, $finder->findFile(ClassFinderTest::class));
     $class = 'Not\\A\\Class';
     $this->assertNull($finder->findFile($class));
 
@@ -31,7 +31,7 @@
     $loader->register();
     $this->assertEquals(__FILE__, $finder->findFile($class));
     // This shouldn't prevent us from finding the original file.
-    $this->assertStringEndsWith($path, $finder->findFile(ClassFinderTest::class));
+    $this->assertStringEndsWith($expected_path, $finder->findFile(ClassFinderTest::class));
 
     // Clean up the additional autoloader after the test.
     $loader->unregister();
diff -u b/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php b/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php
--- b/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php
+++ b/core/tests/Drupal/Tests/Component/Discovery/YamlDirectoryDiscoveryTest.php
@@ -80,6 +80,7 @@
     $discovery = new YamlDirectoryDiscovery($directories, 'test');
     $data = $discovery->findAll();
 
+    // The file path is dependent on the operating system, so we adjust the directory separator.
     $this->assertSame(['id' => 'item1', 'name' => 'test1 item 1', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_1/subdir1' . DIRECTORY_SEPARATOR . 'item_1.test.yml'], $data['test_1']['item1']);
     $this->assertSame(['id' => 'item2', 'name' => 'test1 item 2', YamlDirectoryDiscovery::FILE_KEY => 'vfs://modules/test_1/subdir2' . DIRECTORY_SEPARATOR . 'item_2.test.yml'], $data['test_1']['item2']);
     $this->assertCount(2, $data['test_1']);