Repository: getmoto/moto (python)

Issue:
Elasticsearch not showing created OpenSearch domains
When calling `list_domains` with [boto3: ElasticsearchService ](https://boto3.amazonaws.com/v1/documentation/api/latest/reference/services/es.html) 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 [] != []
```


Pull request description:
Combine functionality ES/OpenSearch
Fixes #8420 

Patch:
diff --git a/moto/es/models.py b/moto/es/models.py
index 4cc65d6fb..729a63f72 100644
--- a/moto/es/models.py
+++ b/moto/es/models.py
@@ -1,155 +1,10 @@
-from typing import Any, Dict, List
-
 from moto.core.base_backend import BackendDict, BaseBackend
-from moto.core.common_models import BaseModel
-from moto.moto_api._internal import mock_random
-from moto.utilities.utils import get_partition
-
-from .exceptions import DomainNotFound
-
-
-class Domain(BaseModel):
-    def __init__(
-        self,
-        region_name: str,
-        domain_name: str,
-        es_version: str,
-        elasticsearch_cluster_config: Dict[str, Any],
-        ebs_options: Dict[str, Any],
-        access_policies: Dict[str, Any],
-        snapshot_options: Dict[str, Any],
-        vpc_options: Dict[str, Any],
-        cognito_options: Dict[str, Any],
-        encryption_at_rest_options: Dict[str, Any],
-        node_to_node_encryption_options: Dict[str, Any],
-        advanced_options: Dict[str, Any],
-        log_publishing_options: Dict[str, Any],
-        domain_endpoint_options: Dict[str, Any],
-        advanced_security_options: Dict[str, Any],
-        auto_tune_options: Dict[str, Any],
-    ):
-        self.domain_id = mock_random.get_random_hex(8)
-        self.region_name = region_name
-        self.domain_name = domain_name
-        self.es_version = es_version
-        self.elasticsearch_cluster_config = elasticsearch_cluster_config
-        self.ebs_options = ebs_options
-        self.access_policies = access_policies
-        self.snapshot_options = snapshot_options
-        self.vpc_options = vpc_options
-        self.cognito_options = cognito_options
-        self.encryption_at_rest_options = encryption_at_rest_options
-        self.node_to_node_encryption_options = node_to_node_encryption_options
-        self.advanced_options = advanced_options
-        self.log_publishing_options = log_publishing_options
-        self.domain_endpoint_options = domain_endpoint_options
-        self.advanced_security_options = advanced_security_options
-        self.auto_tune_options = auto_tune_options
-        if self.auto_tune_options:
-            self.auto_tune_options["State"] = "ENABLED"
-
-    @property
-    def arn(self) -> str:
-        return f"arn:{get_partition(self.region_name)}:es:{self.region_name}:domain/{self.domain_id}"
-
-    def to_json(self) -> Dict[str, Any]:
-        return {
-            "DomainId": self.domain_id,
-            "DomainName": self.domain_name,
-            "ARN": self.arn,
-            "Created": True,
-            "Deleted": False,
-            "Processing": False,
-            "UpgradeProcessing": False,
-            "ElasticsearchVersion": self.es_version,
-            "ElasticsearchClusterConfig": self.elasticsearch_cluster_config,
-            "EBSOptions": self.ebs_options,
-            "AccessPolicies": self.access_policies,
-            "SnapshotOptions": self.snapshot_options,
-            "VPCOptions": self.vpc_options,
-            "CognitoOptions": self.cognito_options,
-            "EncryptionAtRestOptions": self.encryption_at_rest_options,
-            "NodeToNodeEncryptionOptions": self.node_to_node_encryption_options,
-            "AdvancedOptions": self.advanced_options,
-            "LogPublishingOptions": self.log_publishing_options,
-            "DomainEndpointOptions": self.domain_endpoint_options,
-            "AdvancedSecurityOptions": self.advanced_security_options,
-            "AutoTuneOptions": self.auto_tune_options,
-        }
 
 
 class ElasticsearchServiceBackend(BaseBackend):
-    """Implementation of ElasticsearchService APIs."""
-
     def __init__(self, region_name: str, account_id: str):
+        # Functionality is part of OpenSearch, as that includes all of ES functionality + more
         super().__init__(region_name, account_id)
-        self.domains: Dict[str, Domain] = dict()
-
-    def create_elasticsearch_domain(
-        self,
-        domain_name: str,
-        elasticsearch_version: str,
-        elasticsearch_cluster_config: Dict[str, Any],
-        ebs_options: Dict[str, Any],
-        access_policies: Dict[str, Any],
-        snapshot_options: Dict[str, Any],
-        vpc_options: Dict[str, Any],
-        cognito_options: Dict[str, Any],
-        encryption_at_rest_options: Dict[str, Any],
-        node_to_node_encryption_options: Dict[str, Any],
-        advanced_options: Dict[str, Any],
-        log_publishing_options: Dict[str, Any],
-        domain_endpoint_options: Dict[str, Any],
-        advanced_security_options: Dict[str, Any],
-        auto_tune_options: Dict[str, Any],
-    ) -> Dict[str, Any]:
-        # TODO: Persist/Return other attributes
-        new_domain = Domain(
-            region_name=self.region_name,
-            domain_name=domain_name,
-            es_version=elasticsearch_version,
-            elasticsearch_cluster_config=elasticsearch_cluster_config,
-            ebs_options=ebs_options,
-            access_policies=access_policies,
-            snapshot_options=snapshot_options,
-            vpc_options=vpc_options,
-            cognito_options=cognito_options,
-            encryption_at_rest_options=encryption_at_rest_options,
-            node_to_node_encryption_options=node_to_node_encryption_options,
-            advanced_options=advanced_options,
-            log_publishing_options=log_publishing_options,
-            domain_endpoint_options=domain_endpoint_options,
-            advanced_security_options=advanced_security_options,
-            auto_tune_options=auto_tune_options,
-        )
-        self.domains[domain_name] = new_domain
-        return new_domain.to_json()
-
-    def delete_elasticsearch_domain(self, domain_name: str) -> None:
-        if domain_name not in self.domains:
-            raise DomainNotFound(domain_name)
-        del self.domains[domain_name]
-
-    def describe_elasticsearch_domain(self, domain_name: str) -> Dict[str, Any]:
-        if domain_name not in self.domains:
-            raise DomainNotFound(domain_name)
-        return self.domains[domain_name].to_json()
-
-    def list_domain_names(self) -> List[Dict[str, str]]:
-        """
-        The engine-type parameter is not yet supported.
-        Pagination is not yet implemented.
-        """
-        return [{"DomainName": domain.domain_name} for domain in self.domains.values()]
-
-    def describe_elasticsearch_domains(
-        self, domain_names: List[str]
-    ) -> List[Dict[str, Any]]:
-        queried_domains = []
-        for domain_name in domain_names:
-            if domain_name in self.domains:
-                queried_domains.append(self.domains[domain_name].to_json())
-        return queried_domains
 
 
 es_backends = BackendDict(ElasticsearchServiceBackend, "es")
diff --git a/moto/es/responses.py b/moto/es/responses.py
deleted file mode 100644
index 35293b33d..000000000
--- a/moto/es/responses.py
+++ /dev/null
@@ -1,107 +0,0 @@
-import json
-import re
-from typing import Any
-
-from moto.core.common_types import TYPE_RESPONSE
-from moto.core.responses import BaseResponse
-
-from .exceptions import InvalidDomainName
-from .models import ElasticsearchServiceBackend, es_backends
-
-
-class ElasticsearchServiceResponse(BaseResponse):
-    """Handler for ElasticsearchService requests and responses."""
-
-    def __init__(self) -> None:
-        super().__init__(service_name="es")
-
-    @property
-    def es_backend(self) -> ElasticsearchServiceBackend:
-        """Return backend instance specific for this region."""
-        return es_backends[self.current_account][self.region]
-
-    @classmethod
-    def list_domains(cls, request: Any, full_url: str, headers: Any) -> TYPE_RESPONSE:  # type: ignore
-        response = ElasticsearchServiceResponse()
-        response.setup_class(request, full_url, headers)
-        if request.method == "GET":
-            return response.list_domain_names()
-
-    @classmethod
-    def domains(cls, request: Any, full_url: str, headers: Any) -> TYPE_RESPONSE:  # type: ignore
-        response = ElasticsearchServiceResponse()
-        response.setup_class(request, full_url, headers)
-        if request.method == "POST":
-            return response.create_elasticsearch_domain()
-
-    @classmethod
-    def domain(cls, request: Any, full_url: str, headers: Any) -> TYPE_RESPONSE:  # type: ignore
-        response = ElasticsearchServiceResponse()
-        response.setup_class(request, full_url, headers)
-        if request.method == "DELETE":
-            return response.delete_elasticsearch_domain()
-        if request.method == "GET":
-            return response.describe_elasticsearch_domain()
-
-    def create_elasticsearch_domain(self) -> TYPE_RESPONSE:
-        params = json.loads(self.body)
-        domain_name = params.get("DomainName")
-        if not re.match(r"^[a-z][a-z0-9\-]+$", domain_name):
-            raise InvalidDomainName(domain_name)
-        elasticsearch_version = params.get("ElasticsearchVersion")
-        elasticsearch_cluster_config = params.get("ElasticsearchClusterConfig")
-        ebs_options = params.get("EBSOptions")
-        access_policies = params.get("AccessPolicies")
-        snapshot_options = params.get("SnapshotOptions")
-        vpc_options = params.get("VPCOptions")
-        cognito_options = params.get("CognitoOptions")
-        encryption_at_rest_options = params.get("EncryptionAtRestOptions")
-        node_to_node_encryption_options = params.get("NodeToNodeEncryptionOptions")
-        advanced_options = params.get("AdvancedOptions")
-        log_publishing_options = params.get("LogPublishingOptions")
-        domain_endpoint_options = params.get("DomainEndpointOptions")
-        advanced_security_options = params.get("AdvancedSecurityOptions")
-        auto_tune_options = params.get("AutoTuneOptions")
-        domain_status = self.es_backend.create_elasticsearch_domain(
-            domain_name=domain_name,
-            elasticsearch_version=elasticsearch_version,
-            elasticsearch_cluster_config=elasticsearch_cluster_config,
-            ebs_options=ebs_options,
-            access_policies=access_policies,
-            snapshot_options=snapshot_options,
-            vpc_options=vpc_options,
-            cognito_options=cognito_options,
-            encryption_at_rest_options=encryption_at_rest_options,
-            node_to_node_encryption_options=node_to_node_encryption_options,
-            advanced_options=advanced_options,
-            log_publishing_options=log_publishing_options,
-            domain_endpoint_options=domain_endpoint_options,
-            advanced_security_options=advanced_security_options,
-            auto_tune_options=auto_tune_options,
-        )
-        return 200, {}, json.dumps({"DomainStatus": domain_status})
-
-    def delete_elasticsearch_domain(self) -> TYPE_RESPONSE:
-        domain_name = self.path.split("/")[-1]
-        self.es_backend.delete_elasticsearch_domain(domain_name=domain_name)
-        return 200, {}, json.dumps(dict())
-
-    def describe_elasticsearch_domain(self) -> TYPE_RESPONSE:
-        domain_name = self.path.split("/")[-1]
-        if not re.match(r"^[a-z][a-z0-9\-]+$", domain_name):
-            raise InvalidDomainName(domain_name)
-        domain_status = self.es_backend.describe_elasticsearch_domain(
-            domain_name=domain_name
-        )
-        return 200, {}, json.dumps({"DomainStatus": domain_status})
-
-    def list_domain_names(self) -> TYPE_RESPONSE:
-        domain_names = self.es_backend.list_domain_names()
-        return 200, {}, json.dumps({"DomainNames": domain_names})
-
-    def describe_elasticsearch_domains(self) -> TYPE_RESPONSE:
-        domain_names = self._get_param("DomainNames")
-        domain_list = self.es_backend.describe_elasticsearch_domains(
-            domain_names=domain_names,
-        )
-        return 200, {}, json.dumps({"DomainStatusList": domain_list})
diff --git a/moto/es/urls.py b/moto/es/urls.py
index fbee7fcb7..4c1ae5294 100644
--- a/moto/es/urls.py
+++ b/moto/es/urls.py
@@ -1,17 +1,15 @@
 from moto.opensearch.responses import OpenSearchServiceResponse
 
-from .responses import ElasticsearchServiceResponse
-
 url_bases = [
     r"https?://es\.(.+)\.amazonaws\.com",
 ]
 
 
 url_paths = {
-    "{0}/2015-01-01/domain$": ElasticsearchServiceResponse.list_domains,
-    "{0}/2015-01-01/es/domain$": ElasticsearchServiceResponse.domains,
-    "{0}/2015-01-01/es/domain/(?P<domainname>[^/]+)": ElasticsearchServiceResponse.domain,
-    "{0}/2015-01-01/es/domain-info$": ElasticsearchServiceResponse.dispatch,
+    "{0}/2015-01-01/domain$": OpenSearchServiceResponse.list_domains,
+    "{0}/2015-01-01/es/domain$": OpenSearchServiceResponse.domains,
+    "{0}/2015-01-01/es/domain/(?P<domainname>[^/]+)": OpenSearchServiceResponse.domain,
+    "{0}/2015-01-01/es/domain-info$": OpenSearchServiceResponse.list_domains,
     "{0}/2021-01-01/domain$": OpenSearchServiceResponse.dispatch,
     "{0}/2021-01-01/opensearch/compatibleVersions": OpenSearchServiceResponse.dispatch,
     "{0}/2021-01-01/opensearch/domain": OpenSearchServiceResponse.dispatch,
diff --git a/moto/opensearch/exceptions.py b/moto/opensearch/exceptions.py
index 55504a02d..97f9e37ad 100644
--- a/moto/opensearch/exceptions.py
+++ b/moto/opensearch/exceptions.py
@@ -4,6 +4,8 @@ from moto.core.exceptions import JsonRESTError
 
 
 class ResourceNotFoundException(JsonRESTError):
+    code = 409
+
     def __init__(self, name: str):
         super().__init__("ResourceNotFoundException", f"Domain not found: {name}")
 
diff --git a/moto/opensearch/models.py b/moto/opensearch/models.py
index 2e7242983..4927dcbb5 100644
--- a/moto/opensearch/models.py
+++ b/moto/opensearch/models.py
@@ -85,6 +85,9 @@ class OpenSearchDomain(BaseModel):
         auto_tune_options: Dict[str, Any],
         off_peak_window_options: Dict[str, Any],
         software_update_options: Dict[str, bool],
+        is_es: bool,
+        elasticsearch_version: Optional[str],
+        elasticsearch_cluster_config: Optional[str],
     ):
         self.domain_id = f"{account_id}/{domain_name}"
         self.domain_name = domain_name
@@ -113,10 +116,16 @@ class OpenSearchDomain(BaseModel):
             advanced_security_options or default_advanced_security_options
         )
         self.auto_tune_options = auto_tune_options or {"State": "ENABLE_IN_PROGRESS"}
+        if not self.auto_tune_options.get("State"):
+            self.auto_tune_options["State"] = "ENABLED"
         self.off_peak_windows_options = off_peak_window_options
         self.software_update_options = (
             software_update_options or default_software_update_options
         )
+        self.engine_type = "Elasticsearch" if is_es else "OpenSearch"
+        self.is_es = is_es
+        self.elasticsearch_version = elasticsearch_version
+        self.elasticsearch_cluster_config = elasticsearch_cluster_config
 
         self.deleted = False
         self.processing = False
@@ -157,6 +166,8 @@ class OpenSearchDomain(BaseModel):
             "AutoTuneOptions": self.auto_tune_options,
             "OffPeakWindowsOptions": self.off_peak_windows_options,
             "SoftwareUpdateOptions": self.software_update_options,
+            "ElasticsearchVersion": self.elasticsearch_version,
+            "ElasticsearchClusterConfig": self.elasticsearch_cluster_config,
         }
 
     def to_dict(self) -> Dict[str, Any]:
@@ -259,6 +270,9 @@ class OpenSearchServiceBackend(BaseBackend):
         auto_tune_options: Dict[str, Any],
         off_peak_window_options: Dict[str, Any],
         software_update_options: Dict[str, Any],
+        is_es: bool,
+        elasticsearch_version: Optional[str],
+        elasticsearch_cluster_config: Optional[str],
     ) -> OpenSearchDomain:
         domain = OpenSearchDomain(
             account_id=self.account_id,
@@ -280,6 +294,9 @@ class OpenSearchServiceBackend(BaseBackend):
             auto_tune_options=auto_tune_options,
             off_peak_window_options=off_peak_window_options,
             software_update_options=software_update_options,
+            is_es=is_es,
+            elasticsearch_version=elasticsearch_version,
+            elasticsearch_cluster_config=elasticsearch_cluster_config,
         )
         self.domains[domain_name] = domain
         if tag_list:
@@ -355,23 +372,17 @@ class OpenSearchServiceBackend(BaseBackend):
 
     def list_domain_names(self, engine_type: str) -> List[Dict[str, str]]:
         domains = []
+        if engine_type and engine_type not in ["Elasticsearch", "OpenSearch"]:
+            raise EngineTypeNotFoundException(engine_type)
         for domain in self.domains.values():
             if engine_type:
-                if engine_type in domain.engine_version.options:
+                if engine_type == domain.engine_type:
                     domains.append(
-                        {
-                            "DomainName": domain.domain_name,
-                            "EngineType": engine_type.split("_")[0],
-                        }
+                        {"DomainName": domain.domain_name, "EngineType": engine_type}
                     )
-                else:
-                    raise EngineTypeNotFoundException(domain.domain_name)
             else:
                 domains.append(
-                    {
-                        "DomainName": domain.domain_name,
-                        "EngineType": domain.engine_version.options.split("_")[0],
-                    }
+                    {"DomainName": domain.domain_name, "EngineType": domain.engine_type}
                 )
         return domains
 
diff --git a/moto/opensearch/responses.py b/moto/opensearch/responses.py
index 4034a16b2..efb6f9bad 100644
--- a/moto/opensearch/responses.py
+++ b/moto/opensearch/responses.py
@@ -1,8 +1,12 @@
 """Handles incoming opensearch requests, invokes methods, returns responses."""
 
 import json
+import re
+from typing import Any
 
+from moto.core.common_types import TYPE_RESPONSE
 from moto.core.responses import BaseResponse
+from moto.es.exceptions import InvalidDomainName
 
 from .models import OpenSearchServiceBackend, opensearch_backends
 
@@ -18,8 +22,35 @@ class OpenSearchServiceResponse(BaseResponse):
         """Return backend instance specific for this region."""
         return opensearch_backends[self.current_account][self.region]
 
+    @classmethod
+    def list_domains(cls, request: Any, full_url: str, headers: Any) -> TYPE_RESPONSE:  # type: ignore
+        response = cls()
+        response.setup_class(request, full_url, headers)
+        if request.method == "GET":
+            return 200, {}, response.list_domain_names()
+        if request.method == "POST":
+            return 200, {}, response.describe_domains()
+
+    @classmethod
+    def domains(cls, request: Any, full_url: str, headers: Any) -> TYPE_RESPONSE:  # type: ignore
+        response = cls()
+        response.setup_class(request, full_url, headers)
+        if request.method == "POST":
+            return 200, {}, response.create_domain()
+
+    @classmethod
+    def domain(cls, request: Any, full_url: str, headers: Any) -> TYPE_RESPONSE:  # type: ignore
+        response = cls()
+        response.setup_class(request, full_url, headers)
+        if request.method == "DELETE":
+            return 200, {}, response.delete_domain()
+        if request.method == "GET":
+            return 200, {}, response.describe_domain()
+
     def create_domain(self) -> str:
         domain_name = self._get_param("DomainName")
+        if not re.match(r"^[a-z][a-z0-9\-]+$", domain_name):
+            raise InvalidDomainName(domain_name)
         engine_version = self._get_param("EngineVersion")
         cluster_config = self._get_param("ClusterConfig")
         ebs_options = self._get_param("EBSOptions")
@@ -37,6 +68,10 @@ class OpenSearchServiceResponse(BaseResponse):
         auto_tune_options = self._get_param("AutoTuneOptions")
         off_peak_window_options = self._get_param("OffPeakWindowOptions")
         software_update_options = self._get_param("SoftwareUpdateOptions")
+        # ElasticSearch specific options
+        is_es = self.parsed_url.path.endswith("/es/domain")
+        elasticsearch_version = self._get_param("ElasticsearchVersion")
+        elasticsearch_cluster_config = self._get_param("ElasticsearchClusterConfig")
         domain = self.opensearch_backend.create_domain(
             domain_name=domain_name,
             engine_version=engine_version,
@@ -56,6 +91,9 @@ class OpenSearchServiceResponse(BaseResponse):
             auto_tune_options=auto_tune_options,
             off_peak_window_options=off_peak_window_options,
             software_update_options=software_update_options,
+            is_es=is_es,
+            elasticsearch_version=elasticsearch_version,
+            elasticsearch_cluster_config=elasticsearch_cluster_config,
         )
         return json.dumps(dict(DomainStatus=domain.to_dict()))
 
@@ -67,21 +105,23 @@ class OpenSearchServiceResponse(BaseResponse):
         return json.dumps(dict(CompatibleVersions=compatible_versions))
 
     def delete_domain(self) -> str:
-        domain_name = self._get_param("DomainName")
+        domain_name = self.path.split("/")[-1]
         domain = self.opensearch_backend.delete_domain(
             domain_name=domain_name,
         )
         return json.dumps(dict(DomainStatus=domain.to_dict()))
 
     def describe_domain(self) -> str:
-        domain_name = self._get_param("DomainName")
+        domain_name = self.path.split("/")[-1]
+        if not re.match(r"^[a-z][a-z0-9\-]+$", domain_name):
+            raise InvalidDomainName(domain_name)
         domain = self.opensearch_backend.describe_domain(
             domain_name=domain_name,
         )
         return json.dumps(dict(DomainStatus=domain.to_dict()))
 
     def describe_domain_config(self) -> str:
-        domain_name = self._get_param("DomainName")
+        domain_name = self.path.split("/")[-1]
         domain = self.opensearch_backend.describe_domain_config(
             domain_name=domain_name,
         )


Test patch:
diff --git a/tests/test_es/test_es.py b/tests/test_es/test_es.py
index 259f444da..a696d3e39 100644
--- a/tests/test_es/test_es.py
+++ b/tests/test_es/test_es.py
@@ -5,6 +5,7 @@ import pytest
 from botocore.exceptions import ClientError
 
 from moto import mock_aws
+from tests import DEFAULT_ACCOUNT_ID
 
 # See our Development Tips on writing tests for hints on how to write good tests:
 # http://docs.getmoto.org/en/latest/docs/contributing/development_tips/tests.html
@@ -33,7 +34,10 @@ def test_create_elasticsearch_domain_minimal():
 
     domain = resp["DomainStatus"]
     assert domain["DomainName"] == "motosearch"
-    assert domain["ARN"] == f"arn:aws:es:us-east-2:domain/{domain['DomainId']}"
+    assert (
+        domain["ARN"]
+        == f"arn:aws:es:us-east-2:{DEFAULT_ACCOUNT_ID}:domain/{domain['DomainName']}"
+    )
     assert domain["Created"] is True
     assert domain["Deleted"] is False
     assert domain["Processing"] is False
@@ -188,7 +192,10 @@ def test_describe_elasticsearch_domain():
 
     domain = resp["DomainStatus"]
     assert domain["DomainName"] == "motosearch"
-    assert domain["ARN"] == f"arn:aws:es:ap-southeast-1:domain/{domain['DomainId']}"
+    assert (
+        domain["ARN"]
+        == f"arn:aws:es:ap-southeast-1:{DEFAULT_ACCOUNT_ID}:domain/{domain['DomainName']}"
+    )
     assert domain["Created"] is True
     assert domain["Deleted"] is False
     assert domain["Processing"] is False
@@ -204,6 +211,18 @@ def test_list_domain_names_initial():
     assert resp["DomainNames"] == []
 
 
+@mock_aws
+def test_list_domain_names_enginetype():
+    client = boto3.client("es", region_name="us-east-1")
+    client.create_elasticsearch_domain(DomainName="elasticsearch-domain")
+
+    resp = client.list_domain_names(EngineType="Elasticsearch")
+    assert len(resp["DomainNames"]) == 1
+
+    resp = client.list_domain_names(EngineType="OpenSearch")
+    assert len(resp["DomainNames"]) == 0
+
+
 @mock_aws
 def test_list_domain_names_with_multiple_domains():
     client = boto3.client("es", region_name="eu-west-1")
@@ -214,7 +233,9 @@ def test_list_domain_names_with_multiple_domains():
 
     assert len(resp["DomainNames"]) == 4
     for name in domain_names:
-        assert {"DomainName": name} in resp["DomainNames"]
+        assert {"DomainName": name, "EngineType": "Elasticsearch"} in resp[
+            "DomainNames"
+        ]
 
 
 @mock_aws
@@ -240,3 +261,33 @@ def test_describe_elasticsearch_domains():
     # Test for invalid domain name
     resp = client.describe_elasticsearch_domains(DomainNames=["invalid"])
     assert len(resp["DomainStatusList"]) == 0
+
+
+@mock_aws
+def test_list_domain_names_opensearch():
+    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")
+    domain_names = es_client.list_domain_names()["DomainNames"]
+    assert len(domain_names) == 1
+    assert domain_names[0]["DomainName"] == "moto-opensearch"
+    assert domain_names[0]["EngineType"] == "OpenSearch"
+
+
+@mock_aws
+def test_list_domain_names_opensearch_deleted():
+    opensearch_client = boto3.client("opensearch", region_name="us-east-2")
+    opensearch_client.create_domain(DomainName="moto-opensearch")
+    opensearch_client.delete_domain(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"] == []
diff --git a/tests/test_opensearch/test_opensearch.py b/tests/test_opensearch/test_opensearch.py
index 22955de1b..7dd80864a 100644
--- a/tests/test_opensearch/test_opensearch.py
+++ b/tests/test_opensearch/test_opensearch.py
@@ -117,8 +117,17 @@ def test_describe_domain():
 def test_delete_domain():
     client = boto3.client("opensearch", region_name="eu-west-1")
     client.create_domain(DomainName="testdn")
-    client.delete_domain(DomainName="testdn")
+    resp = client.delete_domain(DomainName="testdn")
+    status = resp["DomainStatus"]
+    assert "DomainId" in status
+    assert "DomainName" in status
+    assert status["Deleted"]  # assume deleted completion
+    assert status["DomainName"] == "testdn"
 
+
+@mock_aws
+def test_delete_invalid_domain():
+    client = boto3.client("opensearch", region_name="eu-west-1")
     with pytest.raises(ClientError) as exc:
         client.describe_domain(DomainName="testdn")
     err = exc.value.response["Error"]
@@ -216,7 +225,7 @@ def test_list_unknown_domain_names_engine_type():
         client.list_domain_names(EngineType="unknown")
     err = exc.value.response["Error"]
     assert err["Code"] == "EngineTypeNotFoundException"
-    assert err["Message"] == "Engine Type not found: testdn"
+    assert err["Message"] == "Engine Type not found: unknown"
 
 
 @mock_aws