diff --git a/assets/static/__mocks__/isInViewportMock.js b/assets/static/__mocks__/isInViewportMock.js
index 6c26c9010..9528394d8 100644
--- a/assets/static/__mocks__/isInViewportMock.js
+++ b/assets/static/__mocks__/isInViewportMock.js
@@ -1,11 +1,11 @@
 const $ = require("jquery");
 
-function isInViewport() {}
+// always returns true, indicating that every tested element is in viewport
+function isInViewport() {
+    return true;
+}
 $.extend($.expr[":"], {
     "in-viewport": $.expr.createPseudo
         ? $.expr.createPseudo(argsString => currElement => isInViewport(currElement, argsString))
         : (currObj, index, meta) => isInViewport(currObj, meta)
 })
-
-function run() {}
-$.fn.run = run