Investigated a bit more. The problem is `Menu.prototype.add` is called with three arguments (slug, text, fn) in the test:

```js
.add('Edit item', 'Edit <em>item</em>', function(){ console.log('edit'); })
```
When called with three items, the first is considered the slug. See https://github.com/component/menu/blob/master/index.js#L147