Elasticsearch not showing created OpenSearch domains

[jflim]

When calling list_domains with boto3: ElasticsearchService client, boto3 documentation mentions that the response includes domains of both Elasticsearch or Opensearch.

In my testing, I was able to use the boto3 elasticsearch client to see any OpenSearch domains that were created. But the moto elasticsearch client seems to only track elasticsearch domains.

Here's a test that shows the current results.

@mock_aws
def test_describe_opensearch_domain():
    opensearch_client = boto3.client("opensearch", region_name="us-east-2")
    status = opensearch_client.create_domain(DomainName="moto-opensearch")["DomainStatus"]
    assert status["Created"]
    assert "DomainId" in status
    assert "DomainName" in status
    assert status["DomainName"] == "moto-opensearch"

    # ensure that elasticsearch client can describe opensearch domains as well
    es_client = boto3.client("es", region_name="us-east-2")
    assert es_client.list_domain_names()["DomainNames"] != []

Expected Results

Test passes.

Actual Results

FAILED test_es.py::test_describe_opensearch_domain - assert [] != []