skiplist: Sanity check inserted entries

src/tests/frontend/specs/skiplist.js

@@ -0,0 +1,18 @@
+'use strict';
+
+const SkipList = require('ep_etherpad-lite/static/js/skiplist');
+
+describe('skiplist.js', function () {
+  it('rejects null keys', async function () {
+    const skiplist = new SkipList();
+    for (const key of [undefined, null]) {
+      expect(() => skiplist.push({key})).to.throwError();
+    }
+  });
+
+  it('rejects duplicate keys', async function () {
+    const skiplist = new SkipList();
+    skiplist.push({key: 'foo'});
+    expect(() => skiplist.push({key: 'foo'})).to.throwError();
+  });
+});