diff --git a/tests/llm/services/conftest.py b/tests/llm/services/conftest.py
index 8e128406b2..11c5d8f27c 100644
--- a/tests/llm/services/conftest.py
+++ b/tests/llm/services/conftest.py
@@ -36,7 +36,7 @@ def openai_fixture(openai):
     yield openai
 
 
-@pytest.fixture(name="mock_chat_completion", autouse=True)
+@pytest.fixture(name="mock_chat_completion", autouse=False)
 def mock_chat_completion_fixture(mock_chat_completion):
     yield mock_chat_completion
 
diff --git a/tests/llm/services/test_openai_chat_client.py b/tests/llm/services/test_openai_chat_client.py
index 4976eb1655..aa28643afa 100644
--- a/tests/llm/services/test_openai_chat_client.py
+++ b/tests/llm/services/test_openai_chat_client.py
@@ -14,6 +14,8 @@
 # limitations under the License.
 
 import asyncio
+import openai
+import os
 from unittest import mock
 
 import pytest
@@ -44,6 +46,49 @@ def test_constructor_default_service_constructor(mock_chat_completion: tuple[moc
         mock_client.assert_called_once_with(api_key=None, base_url=None, max_retries=max_retries)
 
 
+@pytest.mark.usefixtures("openai")
+@pytest.mark.parametrize('use_env', [True, False])
+def test_constructor_api_key_base_url(use_env: bool):
+
+    if use_env:
+        env_api_key = "env-12345"
+        env_base_url = "http://env.openai.com/v1/"
+        os.environ["OPENAI_API_KEY"] = env_api_key
+        os.environ["OPENAI_BASE_URL"] = env_base_url
+
+        # Test when api_key and base_url are not passed
+        client = OpenAIChatService().get_client(model_name="test_model")
+        assert client._client.api_key == env_api_key
+        assert str(client._client.base_url) == env_base_url
+
+        # Test when api_key and base_url are passed
+        arg_api_key = "arg-12345"
+        arg_base_url = "http://arg.openai.com/v1/"
+        client = OpenAIChatService(api_key=arg_api_key, base_url=arg_base_url).get_client(model_name="test_model")
+        assert client._client.api_key == arg_api_key
+        assert str(client._client.base_url) == arg_base_url
+    else:
+        os.environ.pop("OPENAI_API_KEY")
+        os.environ.pop("OPENAI_BASE_URL")
+        # Test when api_key and base_url are not passed
+        with pytest.raises(openai.OpenAIError) as excinfo:
+            client = OpenAIChatService().get_client(model_name="test_model")
+
+        assert "api_key client option must be set" in str(excinfo.value)
+
+        # Test when only api_key is passed
+        arg_api_key = "arg-12345"
+        client = OpenAIChatService(api_key=arg_api_key).get_client(model_name="test_model")
+        assert client._client.api_key == arg_api_key
+        assert str(client._client.base_url) == "https://api.openai.com/v1/"
+
+        # Test when both api_key and base_url are passed
+        arg_base_url = "http://arg.openai.com/v1/"
+        client = OpenAIChatService(api_key=arg_api_key, base_url=arg_base_url).get_client(model_name="test_model")
+        assert client._client.api_key == arg_api_key
+        assert str(client._client.base_url) == arg_base_url
+
+
 @pytest.mark.parametrize("use_async", [True, False])
 @pytest.mark.parametrize(
     "input_dict, set_assistant, expected_messages",