Add test for mentioning an account

tests/spec/019-mention.js

@@ -0,0 +1,19 @@
+import {
+  accountProfileMoreOptionsButton, closeDialogButton,
+  getNthDialogOptionsOption, modalDialog
+} from '../utils'
+import { foobarRole } from '../roles'
+
+fixture`019-mention.js`
+  .page`http://localhost:4002`
+
+test('can mention from account profile', async t => {
+  await t.useRole(foobarRole)
+    .navigateTo('/accounts/5')
+    .click(accountProfileMoreOptionsButton)
+    .expect(getNthDialogOptionsOption(1).innerText).contains('Mention @baz')
+    .click(getNthDialogOptionsOption(1))
+    .expect(modalDialog.find('.compose-box-input').value).eql('@baz ')
+    .click(closeDialogButton)
+    .expect(modalDialog.exists).notOk()
+})