diff --git a/google/cloud/datastore/client.py b/google/cloud/datastore/client.py
index e06b8e60..24b53b54 100644
--- a/google/cloud/datastore/client.py
+++ b/google/cloud/datastore/client.py
@@ -60,6 +60,10 @@
 DISABLE_GRPC = "GOOGLE_CLOUD_DISABLE_GRPC"
 """Environment variable acting as flag to disable gRPC."""
 
+_RESERVE_IDS_DEPRECATED_MESSAGE = """\
+Client.reserve_ids is deprecated. Please use \
+Client.reserve_ids_multi or Client.reserve_ids_sequential"""
+
 
 _USE_GRPC = _HAVE_GRPC and not os.getenv(DISABLE_GRPC, False)
 
@@ -890,11 +894,7 @@ def reserve_ids(self, complete_key, num_ids, retry=None, timeout=None):
         Please use either :meth:`reserve_ids_multi` (recommended) or
         :meth:`reserve_ids_sequential`.
         """
-        message = (
-            "Client.reserve_ids is deprecated. Please use "
-            "Client.reserve_ids_multi or Client.reserve_ids_sequential",
-        )
-        warnings.warn(message, DeprecationWarning)
+        warnings.warn(_RESERVE_IDS_DEPRECATED_MESSAGE, DeprecationWarning)
         return self.reserve_ids_sequential(
             complete_key, num_ids, retry=retry, timeout=timeout
         )
diff --git a/tests/unit/test_client.py b/tests/unit/test_client.py
index 59588f10..55a45c7f 100644
--- a/tests/unit/test_client.py
+++ b/tests/unit/test_client.py
@@ -1113,6 +1113,8 @@ def test_reserve_ids_sequential_w_non_numeric_key_name(self):
             client.reserve_ids_sequential(complete_key, num_ids)
 
     def test_reserve_ids_w_completed_key(self):
+        import warnings
+
         num_ids = 2
         creds = _make_credentials()
         client = self._make_one(credentials=creds, _use_grpc=False)
@@ -1122,7 +1124,8 @@ def test_reserve_ids_w_completed_key(self):
         client._datastore_api_internal = ds_api
         self.assertTrue(not complete_key.is_partial)
 
-        client.reserve_ids(complete_key, num_ids)
+        with warnings.catch_warnings(record=True) as warned:
+            client.reserve_ids(complete_key, num_ids)
 
         reserved_keys = (
             _Key(_Key.kind, id)
@@ -1133,7 +1136,12 @@ def test_reserve_ids_w_completed_key(self):
             request={"project_id": self.PROJECT, "keys": expected_keys}
         )
 
+        self.assertEqual(len(warned), 1)
+        self.assertIn("Client.reserve_ids is deprecated.", str(warned[0].message))
+
     def test_reserve_ids_w_completed_key_w_retry_w_timeout(self):
+        import warnings
+
         num_ids = 2
         retry = mock.Mock()
         timeout = 100000
@@ -1146,7 +1154,8 @@ def test_reserve_ids_w_completed_key_w_retry_w_timeout(self):
         ds_api = mock.Mock(reserve_ids=reserve_ids, spec=["reserve_ids"])
         client._datastore_api_internal = ds_api
 
-        client.reserve_ids(complete_key, num_ids, retry=retry, timeout=timeout)
+        with warnings.catch_warnings(record=True) as warned:
+            client.reserve_ids(complete_key, num_ids, retry=retry, timeout=timeout)
 
         reserved_keys = (
             _Key(_Key.kind, id)
@@ -1159,7 +1168,12 @@ def test_reserve_ids_w_completed_key_w_retry_w_timeout(self):
             timeout=timeout,
         )
 
+        self.assertEqual(len(warned), 1)
+        self.assertIn("Client.reserve_ids is deprecated.", str(warned[0].message))
+
     def test_reserve_ids_w_completed_key_w_ancestor(self):
+        import warnings
+
         num_ids = 2
         creds = _make_credentials()
         client = self._make_one(credentials=creds, _use_grpc=False)
@@ -1169,7 +1183,8 @@ def test_reserve_ids_w_completed_key_w_ancestor(self):
         client._datastore_api_internal = ds_api
         self.assertTrue(not complete_key.is_partial)
 
-        client.reserve_ids(complete_key, num_ids)
+        with warnings.catch_warnings(record=True) as warned:
+            client.reserve_ids(complete_key, num_ids)
 
         reserved_keys = (
             _Key("PARENT", "SINGLETON", _Key.kind, id)
@@ -1180,29 +1195,50 @@ def test_reserve_ids_w_completed_key_w_ancestor(self):
             request={"project_id": self.PROJECT, "keys": expected_keys}
         )
 
+        self.assertEqual(len(warned), 1)
+        self.assertIn("Client.reserve_ids is deprecated.", str(warned[0].message))
+
     def test_reserve_ids_w_partial_key(self):
+        import warnings
+
         num_ids = 2
         incomplete_key = _Key(_Key.kind, None)
         creds = _make_credentials()
         client = self._make_one(credentials=creds)
         with self.assertRaises(ValueError):
-            client.reserve_ids(incomplete_key, num_ids)
+            with warnings.catch_warnings(record=True) as warned:
+                client.reserve_ids(incomplete_key, num_ids)
+
+        self.assertEqual(len(warned), 1)
+        self.assertIn("Client.reserve_ids is deprecated.", str(warned[0].message))
 
     def test_reserve_ids_w_wrong_num_ids(self):
+        import warnings
+
         num_ids = "2"
         complete_key = _Key()
         creds = _make_credentials()
         client = self._make_one(credentials=creds)
         with self.assertRaises(ValueError):
-            client.reserve_ids(complete_key, num_ids)
+            with warnings.catch_warnings(record=True) as warned:
+                client.reserve_ids(complete_key, num_ids)
+
+        self.assertEqual(len(warned), 1)
+        self.assertIn("Client.reserve_ids is deprecated.", str(warned[0].message))
 
     def test_reserve_ids_w_non_numeric_key_name(self):
+        import warnings
+
         num_ids = 2
         complete_key = _Key(_Key.kind, "batman")
         creds = _make_credentials()
         client = self._make_one(credentials=creds)
         with self.assertRaises(ValueError):
-            client.reserve_ids(complete_key, num_ids)
+            with warnings.catch_warnings(record=True) as warned:
+                client.reserve_ids(complete_key, num_ids)
+
+        self.assertEqual(len(warned), 1)
+        self.assertIn("Client.reserve_ids is deprecated.", str(warned[0].message))
 
     def test_reserve_ids_multi(self):
         creds = _make_credentials()