Add comprehensive test suite and documentation

- Complete unit, integration, and E2E test coverage (189 test cases)
- Enhanced CI/CD pipeline with race detection and quality checks
- Comprehensive godoc documentation for all packages
- Updated README with API docs, examples, and deployment guides

testdata/test_helper.go

@@ -0,0 +1,53 @@
+package testdata
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+// TestDBPath returns the path to test database files
+func TestDBPath() string {
+	return filepath.Join("testdata")
+}
+
+// CreateTempTestDB creates a temporary test database file
+func CreateTempTestDB(t *testing.T, filename string) string {
+	t.Helper()
+	
+	tempDir := t.TempDir()
+	dbPath := filepath.Join(tempDir, filename)
+	
+	// Create a minimal valid MMDB file header (this is just for testing file operations)
+	// In real tests, we'd use actual MaxMind test database files
+	content := []byte{
+		0xab, 0xcd, 0xef, // Magic bytes for MaxMind DB format
+		0x01, 0x00, 0x00, 0x00, // Version
+	}
+	
+	err := os.WriteFile(dbPath, content, 0644)
+	if err != nil {
+		t.Fatalf("Failed to create test database: %v", err)
+	}
+	
+	return tempDir
+}
+
+// TestIPs contains test IP addresses and their expected countries
+var TestIPs = map[string]string{
+	"8.8.8.8":       "US", // Google DNS
+	"1.1.1.1":       "US", // Cloudflare DNS
+	"199.43.0.43":   "US", // Test IP used in health check
+	"127.0.0.1":     "",   // Localhost - should handle gracefully
+	"192.168.1.1":   "",   // Private IP - should handle gracefully
+	"2001:4860:4860::8888": "US", // Google IPv6 DNS
+}
+
+// InvalidIPs contains invalid IP addresses for testing error handling
+var InvalidIPs = []string{
+	"",
+	"invalid",
+	"256.256.256.256",
+	"1.2.3",
+	"not.an.ip",
+}