How to assign Blog plugin categories to activeMenuItem function?

Question

OctoberCMS

OctoberCms 473, plugin Blog 1.5.2 .

A small problem, tell me how to assign the slug of the Blog plugin categories to the activeMenuItem function (instead of test, respectively):

function onInit() {
$this['activeMenuItem'] = 'test';
}

And maybe someone needs it, the blog categories themselves (id, slug, name) can be displayed in the post like this:

{{ post.categories[0].id }}
or

{% for cat in post.categories %}
  {{ cat.id }}
{% endfor %}