diff --git a/lib/completionlib.php b/lib/completionlib.php
index c705d6194eda1..7f79c950f0820 100644
--- a/lib/completionlib.php
+++ b/lib/completionlib.php
@@ -603,8 +603,8 @@ function internal_get_state($cm, $userid, $current) {
      * @return void
      */
     public function set_module_viewed($cm, $userid=0) {
-        global $PAGE;
-        if ($PAGE->headerprinted) {
+        global $PAGE, $UNITTEST;
+        if ($PAGE->headerprinted && empty($UNITTEST->running)) {
             debugging('set_module_viewed must be called before header is printed',
                     DEBUG_DEVELOPER);
         }