diff --git a/web_src/js/emoji.test.js b/web_src/js/emoji.test.js
new file mode 100644
index 0000000000..55e4787793
--- /dev/null
+++ b/web_src/js/emoji.test.js
@@ -0,0 +1,27 @@
+import {emojiString, emojiHTML} from './features/emoji.js';
+
+test('emojiString', () => {
+  expect(emojiString('+1')).toEqual('👍');
+  expect(emojiString('arrow_right')).toEqual('➡️');
+  expect(emojiString('european_union')).toEqual('🇪🇺');
+  expect(emojiString('eu')).toEqual('🇪🇺');
+
+  expect(emojiString('forgejo')).toEqual(':forgejo:');
+  expect(emojiString('frogejo')).toEqual(':frogejo:');
+  expect(emojiString('blobnom')).toEqual(':blobnom:');
+
+  expect(emojiString('not-a-emoji')).toEqual(':not-a-emoji:');
+});
+
+test('emojiHTML', () => {
+  expect(emojiHTML('+1')).toEqual('<span class="emoji" title=":+1:">👍</span>');
+  expect(emojiHTML('arrow_right')).toEqual('<span class="emoji" title=":arrow_right:">➡️</span>');
+  expect(emojiHTML('european_union')).toEqual('<span class="emoji" title=":european_union:">🇪🇺</span>');
+  expect(emojiHTML('eu')).toEqual('<span class="emoji" title=":eu:">🇪🇺</span>');
+
+  expect(emojiHTML('forgejo')).toEqual('<span class="emoji" title=":forgejo:"><img alt=":forgejo:" src="/assets/img/emoji/forgejo.png"></span>');
+  expect(emojiHTML('frogejo')).toEqual('<span class="emoji" title=":frogejo:"><img alt=":frogejo:" src="/assets/img/emoji/frogejo.png"></span>');
+  expect(emojiHTML('blobnom')).toEqual('<span class="emoji" title=":blobnom:"><img alt=":blobnom:" src="/assets/img/emoji/blobnom.png"></span>');
+
+  expect(emojiHTML('not-a-emoji')).toEqual('<span class="emoji" title=":not-a-emoji:">:not-a-emoji:</span>');
+});
diff --git a/web_src/js/vitest.setup.js b/web_src/js/vitest.setup.js
index 5366958fb5..61a6453cf7 100644
--- a/web_src/js/vitest.setup.js
+++ b/web_src/js/vitest.setup.js
@@ -4,8 +4,9 @@ window.config = {
   csrfToken: 'test-csrf-token-123456',
   pageData: {},
   i18n: {},
-  customEmojis: {},
+  customEmojis: new Set(['forgejo', 'frogejo', 'blobnom']),
   appSubUrl: '',
+  assetUrlPrefix: '/assets',
   mentionValues: [
     {key: 'user1 User 1', value: 'user1', name: 'user1', fullname: 'User 1', avatar: 'https://avatar1.com'},
     {key: 'user2 User 2', value: 'user2', name: 'user2', fullname: 'User 2', avatar: 'https://avatar2.com'},