Add basic unit tests for IP geolocation service

- Test invalid IP validation returns None without API call
- Test caching behavior for repeated calls
- Test error handling for API failures

tests/test_geolocation.py

+import pytest
+from unittest.mock import patch, Mock
+from geolocation import get_ip_country, _ip_country_cache
+
+@pytest.mark.asyncio
+async def test_invalid_ip_validation():
+    """Test that invalid IPs return None without API call"""
+    _ip_country_cache.clear()
+    with patch('httpx.AsyncClient.get') as mock_get:
+        result = await get_ip_country("invalid")
+        assert result is None
+        assert _ip_country_cache["invalid"] is None
+        mock_get.assert_not_called()
+
+@pytest.mark.asyncio
+async def test_caching():
+    """Test that results are cached and repeated calls return cached results"""
+    _ip_country_cache.clear()
+    with patch('httpx.AsyncClient.get') as mock_get:
+        mock_response = Mock()
+        mock_response.status_code = 200
+        mock_response.text = "US"
+        mock_get.return_value = mock_response
+
+        # First call
+        result1 = await get_ip_country("1.1.1.1")
+        assert result1 == "US"
+        assert _ip_country_cache["1.1.1.1"] == "US"
+        mock_get.assert_called_once()
+
+        # Second call should use cache
+        result2 = await get_ip_country("1.1.1.1")
+        assert result2 == "US"
+        mock_get.assert_called_once()  # Still only one call
+
+@pytest.mark.asyncio
+async def test_error_handling():
+    """Test error handling for valid IPs when API fails"""
+    _ip_country_cache.clear()
+    with patch('httpx.AsyncClient.get') as mock_get:
+        mock_get.side_effect = Exception("API fail")
+
+        result = await get_ip_country("1.1.1.1")
+        assert result is None
+        assert _ip_country_cache["1.1.1.1"] is None
+        mock_get.assert_called_once()
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