--- web/core/tests/Drupal/Tests/BrowserTestBase.php.orig	2024-01-09 22:05:30.693134453 -0500
+++ web/core/tests/Drupal/Tests/BrowserTestBase.php	2024-01-09 21:35:05.841690252 -0500
@@ -544,13 +544,28 @@
   public function installDrupal() {
     if (getenv('BROWSERTEST_CACHE_DB')) {
       $this->initDumpFile();
-      if (file_exists($this->dumpFile)) {
+
+      $lock_file = $this->dumpFile . '.lock';
+
+      $this->runWithLockFile($lock_file, function () use (&$install_from_dump) {
+        if (file_exists($this->dumpFile)) {
+          $install_from_dump = TRUE;
+        }
+        else {
+          $this->installDrupalFromProfile();
+          $this->dumpDatabase();
+
+          $install_from_dump = FALSE;
+        }
+      });
+
+      // The check for the dump file happens inside the critical section to
+      // ensure it blocks while a dump is being created, but the installation
+      // happens outside the critical section so that multiple tests can use the
+      // same dump file concurrently.
+      if ($install_from_dump) {
         $this->installDrupalFromDump();
       }
-      else {
-        $this->installDrupalFromProfile();
-        $this->dumpDatabase();
-      }
     }
     else {
       $this->installDrupalFromProfile();
@@ -571,9 +586,58 @@
     }
     sort($modules);
     array_unique($modules);
-    $cache_dir = getenv('BROWSERTEST_CACHE_DIR') ?: sys_get_temp_dir() . '/test_dumps/' . \Drupal::VERSION;
-    is_dir($cache_dir) || mkdir($cache_dir, 0777, TRUE);
-    $this->dumpFile = $cache_dir . '/_' . md5(implode('-', $modules)) . '.sql';
+    $temp_dir = sys_get_temp_dir();
+    $cache_dir = getenv('BROWSERTEST_CACHE_DIR') ?: $temp_dir . '/test_dumps/' . \Drupal::VERSION;
+    $this->dumpFile = $cache_dir . '/' . md5(implode('-', $modules)) . '.sql';
+
+    // Create a folder to contain the test database dumps, if it does not
+    // already exist. Only one test is allowed to create this at a time.
+    $lock_file = sprintf("%s/test_dumps-%s.lock", $temp_dir, \Drupal::VERSION);
+    $this->runWithLockFile($lock_file, function () use ($cache_dir) {
+      if (!is_dir($cache_dir)) {
+        mkdir($cache_dir, 0777, TRUE);
+      }
+    });
+  }
+
+  /**
+   * Acquires an exclusive lock on the specified file and runs the given code.
+   *
+   * This is used to ensure that only one test is executing the same code at the
+   * same time on the same runner. The lock is released after the critical code
+   * returns.
+   *
+   * @param string $lock_file_path
+   *   The path to the lock file.
+   * @param callable $critical_code
+   *   The code to invoke only once the lock is obtained.
+   */
+  private function runWithLockFile(string $lock_file_path, callable $critical_code) {
+    $locked = FALSE;
+    $lock_handle = fopen($lock_file_path, 'w');
+    try {
+      if (($lock_handle !== FALSE) && flock($lock_handle, LOCK_EX)) {
+        $locked = TRUE;
+
+        $critical_code();
+      }
+      else {
+        $this->fail('Failed to acquire lock: ' . $lock_file_path);
+      }
+    }
+    finally {
+      // Delete the lock file before unlocking it to ensure we don't delete a
+      // lock created by another process.
+      if (file_exists($lock_file_path)) {
+        @unlink($lock_file_path);
+      }
+      if ($locked) {
+        @flock($lock_handle, LOCK_UN);
+      }
+      if ($lock_handle !== FALSE) {
+        @fclose($lock_handle);
+      }
+    }
   }
 
   /**