diff --git a/CRM/Core/Smarty.php b/CRM/Core/Smarty.php
index 49a40a4fe3ff..095e9f8bd03d 100644
--- a/CRM/Core/Smarty.php
+++ b/CRM/Core/Smarty.php
@@ -138,7 +138,7 @@ private function initialize() {
     }
 
     $this->register_function('crmURL', ['CRM_Utils_System', 'crmURL']);
-    if (CRM_Utils_Constant::value('CIVICRM_SMARTY_DEFAULT_ESCAPE')) {
+    if (CRM_Utils_Constant::value('CIVICRM_SMARTY_DEFAULT_ESCAPE') || self::isTestEnvironment()) {
       // When default escape is enabled if the core escape is called before
       // any custom escaping is done the modifier_escape function is not
       // found, so require_once straight away. Note this was hit on the basic
@@ -158,6 +158,17 @@ private function initialize() {
     }
   }
 
+  /**
+   * Is this a test environment.
+   *
+   * Currently we just check the class name but it is possible to run tests in CMS frameworks.
+   *
+   * @return bool
+   */
+  private static function isTestEnvironment(): bool {
+    return CRM_Core_Config::singleton()->userFramework === 'UnitTests';
+  }
+
   /**
    * Static instance provider.
    *