diff --git a/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/client.py b/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/client.py
index a28d03aaf8..93519d00ad 100644
--- a/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/client.py
+++ b/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/client.py
@@ -14,7 +14,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
-from google.auth import default, transport
+from google import auth
 from openai import OpenAI as _OpenAI
 
 
@@ -26,10 +26,10 @@ def __new__(cls, **openai_params) -> _OpenAI:
         location = openai_params.get('location')
         project_id = openai_params.get('project_id')
         if project_id:
-            credentials, _ = default()
+            credentials, _ = auth.default()
         else:
-            credentials, project_id = default()
+            credentials, project_id = auth.default()
 
-        credentials.refresh(transport.requests.Request())
+        credentials.refresh(auth.transport.requests.Request())
         base_url = f'https://{location}-aiplatform.googleapis.com/v1beta1/projects/{project_id}/locations/{location}/endpoints/openapi'
         return _OpenAI(api_key=credentials.token, base_url=base_url)
diff --git a/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/model_garden.py b/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/model_garden.py
index e03a801d8a..7b522412ed 100644
--- a/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/model_garden.py
+++ b/py/plugins/vertex-ai/src/genkit/plugins/vertex_ai/model_garden/model_garden.py
@@ -23,8 +23,7 @@
 )
 from genkit.plugins.compat_oai.models.model import OpenAIModel
 from genkit.plugins.compat_oai.typing import OpenAIConfig
-
-from .client import OpenAIClient
+from genkit.plugins.vertex_ai.model_garden.client import OpenAIClient
 
 OPENAI_COMPAT = 'openai-compat'
 MODELGARDEN_PLUGIN_NAME = 'modelgarden'
diff --git a/py/plugins/vertex-ai/tests/model_garden/test_client.py b/py/plugins/vertex-ai/tests/model_garden/test_client.py
new file mode 100644
index 0000000000..58a7fe9371
--- /dev/null
+++ b/py/plugins/vertex-ai/tests/model_garden/test_client.py
@@ -0,0 +1,68 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+"""Unittests for VertexAI Model Garden OpenAI Client."""
+
+from unittest.mock import MagicMock, patch
+
+from genkit.plugins.vertex_ai.model_garden.client import OpenAIClient
+
+
+@patch('google.auth.default')
+@patch('google.auth.transport.requests.Request')
+@patch('openai.OpenAI')
+def test_client_initialization_with_explicit_project_id(mock_openai_cls, mock_request_cls, mock_default_auth):
+    """Unittests for init client."""
+    mock_location = 'location'
+    mock_project_id = 'project_id'
+    mock_token = 'token'
+
+    mock_credentials = MagicMock()
+    mock_credentials.token = mock_token
+
+    mock_default_auth.return_value = (mock_credentials, 'project_id')
+
+    client_instance = OpenAIClient(location=mock_location, project_id=mock_project_id)
+
+    mock_default_auth.assert_called_once()
+    mock_credentials.refresh.assert_called_once()
+    mock_request_cls.assert_called_once()
+
+    assert client_instance is not None
+
+
+@patch('google.auth.default')
+@patch('google.auth.transport.requests.Request')
+@patch('openai.OpenAI')
+def test_client_initialization_without_explicit_project_id(mock_openai_cls, mock_request_cls, mock_default_auth):
+    """Unittests for init client."""
+    mock_location = 'location'
+    mock_token = 'token'
+
+    mock_credentials = MagicMock()
+    mock_credentials.token = mock_token
+
+    mock_default_auth.return_value = (mock_credentials, 'project_id')
+
+    client_instance = OpenAIClient(
+        location=mock_location,
+    )
+
+    mock_default_auth.assert_called_once()
+    mock_credentials.refresh.assert_called_once()
+    mock_request_cls.assert_called_once()
+
+    assert client_instance is not None
diff --git a/py/plugins/vertex-ai/tests/model_garden/test_model_garden.py b/py/plugins/vertex-ai/tests/model_garden/test_model_garden.py
new file mode 100644
index 0000000000..e71ed181d4
--- /dev/null
+++ b/py/plugins/vertex-ai/tests/model_garden/test_model_garden.py
@@ -0,0 +1,87 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+"""Unittests for VertexAI Model Garden Models."""
+
+from unittest.mock import MagicMock, patch
+
+import pytest
+
+from genkit.ai import GenkitRegistry
+from genkit.plugins.vertex_ai.model_garden.model_garden import ModelGarden
+
+
+@pytest.fixture
+@patch('genkit.plugins.vertex_ai.model_garden.model_garden.OpenAIClient')
+def model_garden_instance(client):
+    """Model Garden fixture."""
+    return ModelGarden(
+        model='test', location='us-central1', project_id='project', registry=MagicMock(spec=GenkitRegistry)
+    )
+
+
+@pytest.mark.parametrize(
+    'model_name, expected',
+    [
+        (
+            'meta/llama-3.1-405b-instruct-maas',
+            {
+                'name': 'ModelGarden - Meta - llama-3.1',
+                'supports': {
+                    'constrained': None,
+                    'content_type': None,
+                    'context': None,
+                    'multiturn': True,
+                    'media': False,
+                    'tools': True,
+                    'system_role': True,
+                    'output': [
+                        'json_mode',
+                        'text',
+                    ],
+                    'tool_choice': None,
+                },
+            },
+        ),
+        (
+            'meta/lazaro-model-pro-max',
+            {
+                'name': 'ModelGarden - meta/lazaro-model-pro-max',
+                'supports': {
+                    'constrained': None,
+                    'content_type': None,
+                    'context': None,
+                    'multiturn': True,
+                    'media': True,
+                    'tools': True,
+                    'system_role': True,
+                    'output': [
+                        'json_mode',
+                        'text',
+                    ],
+                    'tool_choice': None,
+                },
+            },
+        ),
+    ],
+)
+def test_get_model_info(model_name, expected, model_garden_instance):
+    """Unittest for get_model_info."""
+    model_garden_instance.name = model_name
+
+    result = model_garden_instance.get_model_info()
+
+    assert result == expected