add mock IntersectionObserver

client/tests/jest/jest-environment.js

@@ -2,12 +2,21 @@ import "jsdom-worker";
 
 import JSDOMEnvironment from "jest-environment-jsdom";
 
+class MockObserver {
+    constructor(...args) {}
+
+    observe(...args) {}
+    unobserve(...args) {}
+}
+
 export default class CustomJSDOMEnvironment extends JSDOMEnvironment {
     constructor(...args) {
         super(...args);
 
         this.global.Worker = Worker;
 
+        this.global.IntersectionObserver = MockObserver;
+
         // FIXME https://github.com/jsdom/jsdom/issues/3363
         this.global.structuredClone = structuredClone;
     }