diff --git a/tests/test_llm_client.py b/tests/test_llm_client.py
new file mode 100644
index 0000000..daeff51
--- /dev/null
+++ b/tests/test_llm_client.py
@@ -0,0 +1,110 @@
+"""Test cases for LLM client."""
+import pytest
+import responses
+
+from app.llm.client import LLMError, call_endpoint_with_messages
+from app.utils.config import LLMEndpoint
+
+
+@responses.activate
+def test_openai_chat():
+    """Test OpenAI chat completion."""
+    # Mock successful response
+    responses.add(
+        responses.POST,
+        "https://api.openai.com/v1/chat/completions",
+        json={
+            "choices": [{
+                "message": {
+                    "role": "assistant",
+                    "content": "Test response"
+                }
+            }]
+        },
+        status=200
+    )
+
+    endpoint = LLMEndpoint(
+        provider="openai",
+        model="gpt-3.5-turbo",
+        api_key="test_key"
+    )
+
+    messages = [{"role": "user", "content": "Test prompt"}]
+    response = call_endpoint_with_messages(endpoint, messages)
+    assert response["choices"][0]["message"]["content"] == "Test response"
+
+
+@responses.activate
+def test_ollama_chat():
+    """Test Ollama chat completion."""
+    # Mock successful response
+    responses.add(
+        responses.POST,
+        "http://localhost:11434/api/chat",
+        json={
+            "message": {
+                "role": "assistant",
+                "content": "Test response"
+            }
+        },
+        status=200
+    )
+
+    endpoint = LLMEndpoint(
+        provider="ollama",
+        model="llama2"
+    )
+
+    messages = [{"role": "user", "content": "Test prompt"}]
+    response = call_endpoint_with_messages(endpoint, messages)
+    assert response["message"]["content"] == "Test response"
+
+
+@responses.activate
+def test_error_handling():
+    """Test error handling."""
+    # Mock error response
+    responses.add(
+        responses.POST,
+        "https://api.openai.com/v1/chat/completions",
+        json={"error": "Test error"},
+        status=400
+    )
+
+    endpoint = LLMEndpoint(
+        provider="openai",
+        model="gpt-3.5-turbo",
+        api_key="test_key"
+    )
+
+    messages = [{"role": "user", "content": "Test prompt"}]
+    with pytest.raises(LLMError):
+        call_endpoint_with_messages(endpoint, messages)
+
+
+def test_endpoint_resolution():
+    """Test endpoint configuration resolution."""
+    # Default Ollama endpoint
+    endpoint = LLMEndpoint(provider="ollama")
+    assert endpoint.model == "llama2"  # Default model
+    assert endpoint.temperature == 0.2  # Default temperature
+
+    # Custom OpenAI endpoint
+    endpoint = LLMEndpoint(
+        provider="openai",
+        model="gpt-4",
+        temperature=0.5,
+        timeout=60
+    )
+    assert endpoint.model == "gpt-4"
+    assert endpoint.temperature == 0.5
+    assert endpoint.timeout == 60
+
+    # Invalid temperature
+    endpoint = LLMEndpoint(temperature=3.0)
+    assert endpoint.temperature == 2.0  # Clamped to max
+
+    # Invalid timeout
+    endpoint = LLMEndpoint(timeout=1.0)
+    assert endpoint.timeout == 5.0  # Clamped to min