Appending to an array in elasticsearch

There isn't a ton of docs about appending to an array so here is a quick example.

Given this mapping inside the index "index_name":

es.indices.create(index='index_name', mappings={
    "dynamic": "strict",
    "properties": {
        "tags": {"type": "keyword"}
    }
})

This is the initial index:

es.index(index="index_name", body={
    "tags": []
})

Append the tag "test" to the "tags" keyword mapping:

self.es.update(index="index_name", id="the elasticsearch id for the initial index above", body={
    "script": {
        "source": "ctx._source.tags.addAll(params.tags)",
        "lang": "painless",
        "params": {
            "tags": ["test"]
        }
    }
})