diff --git a/tests/test_config.py b/tests/test_config.py
new file mode 100644
index 0000000..22fa06a
--- /dev/null
+++ b/tests/test_config.py
@@ -0,0 +1,100 @@
+"""
+Test configuration module for Dolibarr MCP Server.
+"""
+
+import os
+import pytest
+from unittest.mock import patch
+from pathlib import Path
+
+from dolibarr_mcp.config import Config
+
+
+class TestConfig:
+    """Test configuration loading and validation."""
+    
+    def test_config_from_env(self):
+        """Test configuration loading from environment variables."""
+        with patch.dict(os.environ, {
+            'DOLIBARR_URL': 'https://test.dolibarr.com',
+            'DOLIBARR_API_KEY': 'test_key_123',
+            'LOG_LEVEL': 'DEBUG'
+        }):
+            config = Config()
+            assert config.dolibarr_url == 'https://test.dolibarr.com'
+            assert config.dolibarr_api_key == 'test_key_123'
+            assert config.log_level == 'DEBUG'
+    
+    def test_config_defaults(self):
+        """Test configuration defaults when env vars not set."""
+        with patch.dict(os.environ, {}, clear=True):
+            config = Config()
+            assert config.log_level == 'INFO'  # Default log level
+    
+    def test_config_validation(self):
+        """Test configuration validation."""
+        with patch.dict(os.environ, {
+            'DOLIBARR_URL': '',
+            'DOLIBARR_API_KEY': ''
+        }):
+            with pytest.raises(ValueError, match="DOLIBARR_URL must be configured"):
+                config = Config()
+                config.validate()
+    
+    def test_config_url_normalization(self):
+        """Test URL normalization (removing trailing slashes)."""
+        with patch.dict(os.environ, {
+            'DOLIBARR_URL': 'https://test.dolibarr.com/',
+            'DOLIBARR_API_KEY': 'test_key'
+        }):
+            config = Config()
+            assert config.dolibarr_url == 'https://test.dolibarr.com'
+            assert not config.dolibarr_url.endswith('/')
+    
+    def test_config_from_dotenv(self, tmp_path):
+        """Test configuration loading from .env file."""
+        env_file = tmp_path / ".env"
+        env_file.write_text(
+            "DOLIBARR_URL=https://env.dolibarr.com\n"
+            "DOLIBARR_API_KEY=env_key_456\n"
+            "LOG_LEVEL=WARNING\n"
+        )
+        
+        with patch.dict(os.environ, {'DOTENV_PATH': str(env_file)}):
+            config = Config()
+            assert config.dolibarr_url == 'https://env.dolibarr.com'
+            assert config.dolibarr_api_key == 'env_key_456'
+            assert config.log_level == 'WARNING'
+    
+    def test_config_precedence(self):
+        """Test that environment variables take precedence over .env file."""
+        with patch.dict(os.environ, {
+            'DOLIBARR_URL': 'https://env.dolibarr.com',
+            'DOLIBARR_API_KEY': 'env_key'
+        }):
+            config = Config()
+            assert config.dolibarr_url == 'https://env.dolibarr.com'
+            assert config.dolibarr_api_key == 'env_key'
+    
+    def test_log_level_validation(self):
+        """Test log level validation."""
+        valid_levels = ['DEBUG', 'INFO', 'WARNING', 'ERROR', 'CRITICAL']
+        
+        for level in valid_levels:
+            with patch.dict(os.environ, {
+                'DOLIBARR_URL': 'https://test.com',
+                'DOLIBARR_API_KEY': 'key',
+                'LOG_LEVEL': level
+            }):
+                config = Config()
+                assert config.log_level == level
+    
+    def test_invalid_log_level(self):
+        """Test invalid log level falls back to default."""
+        with patch.dict(os.environ, {
+            'DOLIBARR_URL': 'https://test.com',
+            'DOLIBARR_API_KEY': 'key',
+            'LOG_LEVEL': 'INVALID'
+        }):
+            config = Config()
+            assert config.log_level == 'INFO'  # Should fall back to default