diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..723a254
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,24 @@
+[run]
+source = gemini_server
+omit = 
+    */tests/*
+    */venv/*
+    */__pycache__/*
+    */site-packages/*
+
+[report]
+exclude_lines =
+    pragma: no cover
+    def __repr__
+    if self.debug:
+    if settings.DEBUG
+    raise AssertionError
+    raise NotImplementedError
+    if 0:
+    if __name__ == .__main__.:
+    if TYPE_CHECKING:
+    class .*\bProtocol\):
+    @(abc\.)?abstractmethod
+
+[html]
+directory = htmlcov
\ No newline at end of file
diff --git a/.github/workflows/test.yml b/.github/workflows/test.yml
new file mode 100644
index 0000000..239bc8f
--- /dev/null
+++ b/.github/workflows/test.yml
@@ -0,0 +1,80 @@
+name: Test
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  test:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        python-version: ['3.8', '3.9', '3.10', '3.11', '3.12']
+
+    steps:
+    - uses: actions/checkout@v4
+
+    - name: Set up Python ${{ matrix.python-version }}
+      uses: actions/setup-python@v5
+      with:
+        python-version: ${{ matrix.python-version }}
+
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install -r requirements.txt
+
+    - name: Run tests with pytest
+      env:
+        GEMINI_API_KEY: "dummy-key-for-tests"
+      run: |
+        pytest tests/ -v --cov=gemini_server --cov-report=xml --cov-report=term
+
+    - name: Upload coverage to Codecov
+      if: matrix.os == 'ubuntu-latest' && matrix.python-version == '3.11'
+      uses: codecov/codecov-action@v4
+      with:
+        file: ./coverage.xml
+        flags: unittests
+        name: codecov-umbrella
+        fail_ci_if_error: false
+
+  lint:
+    runs-on: ubuntu-latest
+    
+    steps:
+    - uses: actions/checkout@v4
+    
+    - name: Set up Python
+      uses: actions/setup-python@v5
+      with:
+        python-version: '3.11'
+    
+    - name: Install dependencies
+      run: |
+        python -m pip install --upgrade pip
+        pip install flake8 black isort mypy
+        pip install -r requirements.txt
+    
+    - name: Lint with flake8
+      run: |
+        # Stop the build if there are Python syntax errors or undefined names
+        flake8 gemini_server.py --count --select=E9,F63,F7,F82 --show-source --statistics
+        # exit-zero treats all errors as warnings
+        flake8 gemini_server.py --count --exit-zero --max-complexity=10 --max-line-length=120 --statistics
+    
+    - name: Check formatting with black
+      run: |
+        black --check gemini_server.py
+    
+    - name: Check import order with isort
+      run: |
+        isort --check-only gemini_server.py
+    
+    - name: Type check with mypy
+      run: |
+        mypy gemini_server.py --ignore-missing-imports
\ No newline at end of file
diff --git a/.gitignore b/.gitignore
index 04cd3c4..ba48462 100644
--- a/.gitignore
+++ b/.gitignore
@@ -154,4 +154,8 @@ cython_debug/
 
 # Test outputs
 test_output/
-*.test.log
\ No newline at end of file
+*.test.log
+.coverage
+htmlcov/
+coverage.xml
+.pytest_cache/
\ No newline at end of file
diff --git a/README.md b/README.md
index 857c854..0ba57c4 100644
--- a/README.md
+++ b/README.md
@@ -231,10 +231,49 @@ Claude: [refines based on feedback]
 - Token estimation: ~4 characters per token
 - All file paths should be absolute paths
 
+## 🧪 Testing
+
+### Running Tests Locally
+
+```bash
+# Install development dependencies
+pip install -r requirements.txt
+
+# Run tests with coverage
+pytest
+
+# Run tests with verbose output
+pytest -v
+
+# Run specific test file
+pytest tests/test_gemini_server.py
+
+# Generate HTML coverage report
+pytest --cov-report=html
+open htmlcov/index.html  # View coverage report
+```
+
+### Continuous Integration
+
+This project uses GitHub Actions for automated testing:
+- Tests run on every push and pull request
+- Supports Python 3.8 - 3.12
+- Tests on Ubuntu, macOS, and Windows
+- Includes linting with flake8, black, isort, and mypy
+- Maintains 80%+ code coverage
+
 ## 🤝 Contributing
 
 This server is designed specifically for Claude Code users. Contributions that enhance the developer experience are welcome!
 
+1. Fork the repository
+2. Create a feature branch (`git checkout -b feature/amazing-feature`)
+3. Write tests for your changes
+4. Ensure all tests pass (`pytest`)
+5. Commit your changes (`git commit -m 'Add amazing feature'`)
+6. Push to the branch (`git push origin feature/amazing-feature`)
+7. Open a Pull Request
+
 ## 📄 License
 
 MIT License - feel free to customize for your development workflow.
\ No newline at end of file
diff --git a/pytest.ini b/pytest.ini
new file mode 100644
index 0000000..11fbe5d
--- /dev/null
+++ b/pytest.ini
@@ -0,0 +1,14 @@
+[pytest]
+testpaths = tests
+python_files = test_*.py
+python_classes = Test*
+python_functions = test_*
+asyncio_mode = auto
+addopts = 
+    -v
+    --strict-markers
+    --tb=short
+    --cov=gemini_server
+    --cov-report=term-missing
+    --cov-report=html
+    --cov-fail-under=80
\ No newline at end of file
diff --git a/requirements.txt b/requirements.txt
index 7a7a6b2..ba7f9eb 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -1,3 +1,9 @@
 mcp>=1.0.0
 google-generativeai>=0.8.0
-python-dotenv>=1.0.0
\ No newline at end of file
+python-dotenv>=1.0.0
+
+# Development dependencies
+pytest>=7.4.0
+pytest-asyncio>=0.21.0
+pytest-cov>=4.1.0
+pytest-mock>=3.11.0
\ No newline at end of file
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..76714ee
--- /dev/null
+++ b/tests/__init__.py
@@ -0,0 +1 @@
+# Tests for Gemini MCP Server
\ No newline at end of file
diff --git a/tests/test_gemini_server.py b/tests/test_gemini_server.py
new file mode 100644
index 0000000..fb6aaff
--- /dev/null
+++ b/tests/test_gemini_server.py
@@ -0,0 +1,275 @@
+"""
+Unit tests for Gemini MCP Server
+"""
+
+import pytest
+import json
+from unittest.mock import Mock, patch, AsyncMock
+from pathlib import Path
+import sys
+
+# Add parent directory to path for imports
+sys.path.append(str(Path(__file__).parent.parent))
+
+from gemini_server import (
+    GeminiChatRequest,
+    CodeAnalysisRequest,
+    read_file_content,
+    prepare_code_context,
+    handle_list_tools,
+    handle_call_tool,
+    DEVELOPER_SYSTEM_PROMPT,
+    DEFAULT_MODEL
+)
+
+
+class TestModels:
+    """Test request models"""
+    
+    def test_gemini_chat_request_defaults(self):
+        """Test GeminiChatRequest with default values"""
+        request = GeminiChatRequest(prompt="Test prompt")
+        assert request.prompt == "Test prompt"
+        assert request.system_prompt is None
+        assert request.max_tokens == 8192
+        assert request.temperature == 0.5
+        assert request.model == DEFAULT_MODEL
+    
+    def test_gemini_chat_request_custom(self):
+        """Test GeminiChatRequest with custom values"""
+        request = GeminiChatRequest(
+            prompt="Test prompt",
+            system_prompt="Custom system",
+            max_tokens=4096,
+            temperature=0.8,
+            model="custom-model"
+        )
+        assert request.system_prompt == "Custom system"
+        assert request.max_tokens == 4096
+        assert request.temperature == 0.8
+        assert request.model == "custom-model"
+    
+    def test_code_analysis_request_defaults(self):
+        """Test CodeAnalysisRequest with default values"""
+        request = CodeAnalysisRequest(question="Analyze this")
+        assert request.question == "Analyze this"
+        assert request.files is None
+        assert request.code is None
+        assert request.max_tokens == 8192
+        assert request.temperature == 0.2
+        assert request.model == DEFAULT_MODEL
+
+
+class TestFileOperations:
+    """Test file reading and context preparation"""
+    
+    def test_read_file_content_success(self, tmp_path):
+        """Test successful file reading"""
+        test_file = tmp_path / "test.py"
+        test_file.write_text("def hello():\n    return 'world'")
+        
+        content = read_file_content(str(test_file))
+        assert "=== File:" in content
+        assert "def hello():" in content
+        assert "return 'world'" in content
+    
+    def test_read_file_content_not_found(self):
+        """Test reading non-existent file"""
+        content = read_file_content("/nonexistent/file.py")
+        assert "Error: File not found" in content
+    
+    def test_read_file_content_directory(self, tmp_path):
+        """Test reading a directory instead of file"""
+        content = read_file_content(str(tmp_path))
+        assert "Error: Not a file" in content
+    
+    def test_prepare_code_context_with_files(self, tmp_path):
+        """Test preparing context from files"""
+        file1 = tmp_path / "file1.py"
+        file1.write_text("print('file1')")
+        file2 = tmp_path / "file2.py"
+        file2.write_text("print('file2')")
+        
+        context = prepare_code_context([str(file1), str(file2)], None)
+        assert "file1.py" in context
+        assert "file2.py" in context
+        assert "print('file1')" in context
+        assert "print('file2')" in context
+    
+    def test_prepare_code_context_with_code(self):
+        """Test preparing context from direct code"""
+        code = "def test():\n    pass"
+        context = prepare_code_context(None, code)
+        assert "=== Direct Code ===" in context
+        assert code in context
+    
+    def test_prepare_code_context_mixed(self, tmp_path):
+        """Test preparing context from both files and code"""
+        test_file = tmp_path / "test.py"
+        test_file.write_text("# From file")
+        code = "# Direct code"
+        
+        context = prepare_code_context([str(test_file)], code)
+        assert "# From file" in context
+        assert "# Direct code" in context
+
+
+class TestToolHandlers:
+    """Test MCP tool handlers"""
+    
+    @pytest.mark.asyncio
+    async def test_handle_list_tools(self):
+        """Test listing available tools"""
+        tools = await handle_list_tools()
+        assert len(tools) == 3
+        
+        tool_names = [tool.name for tool in tools]
+        assert "chat" in tool_names
+        assert "analyze_code" in tool_names
+        assert "list_models" in tool_names
+    
+    @pytest.mark.asyncio
+    async def test_handle_call_tool_unknown(self):
+        """Test calling unknown tool"""
+        result = await handle_call_tool("unknown_tool", {})
+        assert len(result) == 1
+        assert "Unknown tool" in result[0].text
+    
+    @pytest.mark.asyncio
+    @patch('gemini_server.genai.GenerativeModel')
+    async def test_handle_call_tool_chat_success(self, mock_model):
+        """Test successful chat tool call"""
+        # Mock the response
+        mock_response = Mock()
+        mock_response.candidates = [Mock()]
+        mock_response.candidates[0].content.parts = [Mock(text="Test response")]
+        
+        mock_instance = Mock()
+        mock_instance.generate_content.return_value = mock_response
+        mock_model.return_value = mock_instance
+        
+        result = await handle_call_tool("chat", {
+            "prompt": "Test prompt",
+            "temperature": 0.5
+        })
+        
+        assert len(result) == 1
+        assert result[0].text == "Test response"
+        
+        # Verify model was called with correct parameters
+        mock_model.assert_called_once()
+        call_args = mock_model.call_args[1]
+        assert call_args['model_name'] == DEFAULT_MODEL
+        assert call_args['generation_config']['temperature'] == 0.5
+    
+    @pytest.mark.asyncio
+    @patch('gemini_server.genai.GenerativeModel')
+    async def test_handle_call_tool_chat_with_developer_prompt(self, mock_model):
+        """Test chat tool uses developer prompt when no system prompt provided"""
+        mock_response = Mock()
+        mock_response.candidates = [Mock()]
+        mock_response.candidates[0].content.parts = [Mock(text="Response")]
+        
+        mock_instance = Mock()
+        mock_instance.generate_content.return_value = mock_response
+        mock_model.return_value = mock_instance
+        
+        await handle_call_tool("chat", {"prompt": "Test"})
+        
+        # Check that developer prompt was included
+        call_args = mock_instance.generate_content.call_args[0][0]
+        assert DEVELOPER_SYSTEM_PROMPT in call_args
+    
+    @pytest.mark.asyncio
+    async def test_handle_call_tool_analyze_code_no_input(self):
+        """Test analyze_code with no files or code"""
+        result = await handle_call_tool("analyze_code", {
+            "question": "Analyze what?"
+        })
+        assert len(result) == 1
+        assert "Must provide either 'files' or 'code'" in result[0].text
+    
+    @pytest.mark.asyncio
+    @patch('gemini_server.genai.GenerativeModel')
+    async def test_handle_call_tool_analyze_code_success(self, mock_model, tmp_path):
+        """Test successful code analysis"""
+        # Create test file
+        test_file = tmp_path / "test.py"
+        test_file.write_text("def hello(): pass")
+        
+        # Mock response
+        mock_response = Mock()
+        mock_response.candidates = [Mock()]
+        mock_response.candidates[0].content.parts = [Mock(text="Analysis result")]
+        
+        mock_instance = Mock()
+        mock_instance.generate_content.return_value = mock_response
+        mock_model.return_value = mock_instance
+        
+        result = await handle_call_tool("analyze_code", {
+            "files": [str(test_file)],
+            "question": "Analyze this"
+        })
+        
+        assert len(result) == 1
+        assert result[0].text == "Analysis result"
+    
+    @pytest.mark.asyncio
+    @patch('gemini_server.genai.list_models')
+    async def test_handle_call_tool_list_models(self, mock_list_models):
+        """Test listing models"""
+        # Mock model data
+        mock_model = Mock()
+        mock_model.name = "test-model"
+        mock_model.display_name = "Test Model"
+        mock_model.description = "A test model"
+        mock_model.supported_generation_methods = ['generateContent']
+        
+        mock_list_models.return_value = [mock_model]
+        
+        result = await handle_call_tool("list_models", {})
+        assert len(result) == 1
+        
+        models = json.loads(result[0].text)
+        assert len(models) == 1
+        assert models[0]['name'] == "test-model"
+        assert models[0]['is_default'] == False
+
+
+class TestErrorHandling:
+    """Test error handling scenarios"""
+    
+    @pytest.mark.asyncio
+    @patch('gemini_server.genai.GenerativeModel')
+    async def test_handle_call_tool_chat_api_error(self, mock_model):
+        """Test handling API errors in chat"""
+        mock_instance = Mock()
+        mock_instance.generate_content.side_effect = Exception("API Error")
+        mock_model.return_value = mock_instance
+        
+        result = await handle_call_tool("chat", {"prompt": "Test"})
+        assert len(result) == 1
+        assert "Error calling Gemini API" in result[0].text
+        assert "API Error" in result[0].text
+    
+    @pytest.mark.asyncio
+    @patch('gemini_server.genai.GenerativeModel')
+    async def test_handle_call_tool_chat_blocked_response(self, mock_model):
+        """Test handling blocked responses"""
+        mock_response = Mock()
+        mock_response.candidates = [Mock()]
+        mock_response.candidates[0].content.parts = []
+        mock_response.candidates[0].finish_reason = 2
+        
+        mock_instance = Mock()
+        mock_instance.generate_content.return_value = mock_response
+        mock_model.return_value = mock_instance
+        
+        result = await handle_call_tool("chat", {"prompt": "Test"})
+        assert len(result) == 1
+        assert "Response blocked or incomplete" in result[0].text
+        assert "Finish reason: 2" in result[0].text
+
+
+if __name__ == "__main__":
+    pytest.main([__file__, "-v"])
\ No newline at end of file