add rootResourceId to RestAPI responses

moto/apigateway/models.py

@@ -1021,6 +1021,7 @@ class RestAPI(CloudFormationModel):
     PROP_POLICY = "policy"
     PROP_DISABLE_EXECUTE_API_ENDPOINT = "disableExecuteApiEndpoint"
     PROP_MINIMUM_COMPRESSION_SIZE = "minimumCompressionSize"
+    PROP_ROOT_RESOURCE_ID = "rootResourceId"
 
     # operations
     OPERATION_ADD = "add"
@@ -1065,6 +1066,7 @@ def __init__(
         self.models: Dict[str, Model] = {}
         self.request_validators: Dict[str, RequestValidator] = {}
         self.default = self.add_child("/")  # Add default child
+        self.root_resource_id = self.default.id
 
     def __repr__(self) -> str:
         return str(self.id)
@@ -1083,6 +1085,7 @@ def to_dict(self) -> Dict[str, Any]:
             self.PROP_POLICY: self.policy,
             self.PROP_DISABLE_EXECUTE_API_ENDPOINT: self.disableExecuteApiEndpoint,
             self.PROP_MINIMUM_COMPRESSION_SIZE: self.minimum_compression_size,
+            self.PROP_ROOT_RESOURCE_ID: self.root_resource_id,
         }
 
     def apply_patch_operations(self, patch_operations: List[Dict[str, Any]]) -> None:

tests/test_apigateway/test_apigateway.py

@@ -19,6 +19,7 @@ def test_create_and_get_rest_api():
         name="my_api", description="this is my api", disableExecuteApiEndpoint=True
     )
     api_id = response["id"]
+    root_resource_id = response["rootResourceId"]
 
     response = client.get_rest_api(restApiId=api_id)
 
@@ -34,6 +35,7 @@ def test_create_and_get_rest_api():
         "endpointConfiguration": {"types": ["EDGE"]},
         "tags": {},
         "disableExecuteApiEndpoint": True,
+        "rootResourceId": root_resource_id,
     }
 
 
@@ -42,6 +44,7 @@ def test_update_rest_api():
     client = boto3.client("apigateway", region_name="us-west-2")
     response = client.create_rest_api(name="my_api", description="this is my api")
     api_id = response["id"]
+    root_resource_id = response["rootResourceId"]
     patchOperations = [
         {"op": "replace", "path": "/name", "value": "new-name"},
         {"op": "replace", "path": "/description", "value": "new-description"},
@@ -71,6 +74,7 @@ def test_update_rest_api():
         "endpointConfiguration": {"types": ["EDGE"]},
         "tags": {},
         "disableExecuteApiEndpoint": True,
+        "rootResourceId": root_resource_id,
     }
     # should fail with wrong apikeysoruce
     patchOperations = [