going full courtside

2026-02-27 17:33:40 -05:00
parent 6d11b273f1
commit c99d31feff
24 changed files with 1569 additions and 220 deletions
--- a/backend-go/internal/config/config.go
+++ b/backend-go/internal/config/config.go
@@ -20,6 +20,12 @@ type Config struct {
 	EthRPCURL         string
 	PollIntervalMS    int
 	NodeEnv           string
+
+	SMTPHost     string
+	SMTPPort     int
+	SMTPUser     string
+	SMTPPassword string
+	SMTPFrom     string
 }

 func Load() (*Config, error) {
@@ -36,6 +42,12 @@ func Load() (*Config, error) {
 		EthRPCURL:      os.Getenv("ETH_RPC_URL"),
 		PollIntervalMS: getEnvInt("POLL_INTERVAL_MS", 60000),
 		NodeEnv:        getEnv("NODE_ENV", "development"),
+
+		SMTPHost:     os.Getenv("SMTP_HOST"),
+		SMTPPort:     getEnvInt("SMTP_PORT", 587),
+		SMTPUser:     os.Getenv("SMTP_USER"),
+		SMTPPassword: os.Getenv("SMTP_PASSWORD"),
+		SMTPFrom:     os.Getenv("SMTP_FROM"),
 	}

 	if cfg.PollIntervalMS < 1000 {
--- a/backend-go/internal/config/config_test.go
+++ b/backend-go/internal/config/config_test.go
@@ -0,0 +1,115 @@
+package config
+
+import (
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestLoad_Defaults(t *testing.T) {
+	for _, key := range []string{"PORT", "API_BASE_PATH", "POLL_INTERVAL_MS", "NODE_ENV", "SMTP_PORT"} {
+		os.Unsetenv(key)
+	}
+
+	cfg, err := Load()
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	if cfg.Port != 3001 {
+		t.Errorf("Port = %d, want 3001", cfg.Port)
+	}
+	if cfg.APIBasePath != "/v1" {
+		t.Errorf("APIBasePath = %q, want /v1", cfg.APIBasePath)
+	}
+	if cfg.PollIntervalMS != 60000 {
+		t.Errorf("PollIntervalMS = %d, want 60000", cfg.PollIntervalMS)
+	}
+	if cfg.NodeEnv != "development" {
+		t.Errorf("NodeEnv = %q, want development", cfg.NodeEnv)
+	}
+	if cfg.SMTPPort != 587 {
+		t.Errorf("SMTPPort = %d, want 587", cfg.SMTPPort)
+	}
+}
+
+func TestLoad_InvalidPollInterval(t *testing.T) {
+	os.Setenv("POLL_INTERVAL_MS", "500")
+	defer os.Unsetenv("POLL_INTERVAL_MS")
+
+	_, err := Load()
+	if err == nil {
+		t.Fatal("expected error for poll interval < 1000")
+	}
+}
+
+func TestDSN_DatabaseURL(t *testing.T) {
+	cfg := &Config{DatabaseURL: "postgres://user:pass@localhost/db"}
+	dsn := cfg.DSN()
+	if !strings.Contains(dsn, "sslmode=disable") {
+		t.Error("DSN should append sslmode=disable")
+	}
+	if !strings.HasPrefix(dsn, "postgres://user:pass@localhost/db") {
+		t.Error("DSN should preserve original URL")
+	}
+}
+
+func TestDSN_DatabaseURL_WithSSLMode(t *testing.T) {
+	cfg := &Config{DatabaseURL: "postgres://user:pass@localhost/db?sslmode=require"}
+	dsn := cfg.DSN()
+	if strings.Count(dsn, "sslmode=") != 1 {
+		t.Error("DSN should not duplicate sslmode")
+	}
+}
+
+func TestDSN_Components(t *testing.T) {
+	cfg := &Config{
+		DBHost:     "myhost",
+		DBPort:     5433,
+		DBUser:     "myuser",
+		DBPassword: "mypass",
+		DBName:     "mydb",
+	}
+	dsn := cfg.DSN()
+	if !strings.Contains(dsn, "host=myhost") {
+		t.Error("DSN should contain host")
+	}
+	if !strings.Contains(dsn, "port=5433") {
+		t.Error("DSN should contain port")
+	}
+	if !strings.Contains(dsn, "user=myuser") {
+		t.Error("DSN should contain user")
+	}
+	if !strings.Contains(dsn, "dbname=mydb") {
+		t.Error("DSN should contain dbname")
+	}
+}
+
+func TestGetEnv(t *testing.T) {
+	os.Setenv("TEST_KEY_KOINPING", "value")
+	defer os.Unsetenv("TEST_KEY_KOINPING")
+
+	if got := getEnv("TEST_KEY_KOINPING", "fallback"); got != "value" {
+		t.Errorf("got %q, want %q", got, "value")
+	}
+	if got := getEnv("NONEXISTENT_KEY_KOINPING", "fallback"); got != "fallback" {
+		t.Errorf("got %q, want %q", got, "fallback")
+	}
+}
+
+func TestGetEnvInt(t *testing.T) {
+	os.Setenv("TEST_INT_KOINPING", "42")
+	defer os.Unsetenv("TEST_INT_KOINPING")
+
+	if got := getEnvInt("TEST_INT_KOINPING", 0); got != 42 {
+		t.Errorf("got %d, want 42", got)
+	}
+	if got := getEnvInt("NONEXISTENT_INT_KOINPING", 99); got != 99 {
+		t.Errorf("got %d, want 99", got)
+	}
+
+	os.Setenv("TEST_INT_KOINPING", "notanumber")
+	if got := getEnvInt("TEST_INT_KOINPING", 99); got != 99 {
+		t.Errorf("got %d, want 99 for invalid int", got)
+	}
+}
--- a/backend-go/internal/domain/types.go
+++ b/backend-go/internal/domain/types.go
@@ -82,12 +82,11 @@ type CheckpointDetail struct {
 }

 type NotificationConfig struct {
-	UserID              string  `json:"user_id"`
-	DiscordWebhookURL   *string `json:"discord_webhook_url"`
-	TelegramChatID      *string `json:"telegram_chat_id"`
-	TelegramBotToken    *string `json:"telegram_bot_token,omitempty"`
-	Email               *string `json:"email"`
-	NotificationEnabled bool    `json:"notification_enabled"`
+	UserID              string     `json:"user_id"`
+	DiscordWebhookURL   *string    `json:"discord_webhook_url"`
+	SlackWebhookURL     *string    `json:"slack_webhook_url"`
+	Email               *string    `json:"email"`
+	NotificationEnabled bool       `json:"notification_enabled"`
 	CreatedAt           *time.Time `json:"created_at,omitempty"`
 	UpdatedAt           *time.Time `json:"updated_at,omitempty"`
 }
--- a/backend-go/internal/domain/types_test.go
+++ b/backend-go/internal/domain/types_test.go
@@ -0,0 +1,35 @@
+package domain
+
+import "testing"
+
+func TestIsValidAlertType(t *testing.T) {
+	valid := []string{"incoming_tx", "outgoing_tx", "large_transfer", "balance_below"}
+	for _, v := range valid {
+		if !IsValidAlertType(v) {
+			t.Errorf("IsValidAlertType(%q) = false, want true", v)
+		}
+	}
+
+	invalid := []string{"", "invalid", "INCOMING_TX", "send", "receive"}
+	for _, v := range invalid {
+		if IsValidAlertType(v) {
+			t.Errorf("IsValidAlertType(%q) = true, want false", v)
+		}
+	}
+}
+
+func TestIsThresholdRequired(t *testing.T) {
+	required := []AlertType{AlertLargeTransfer, AlertBalanceBelow}
+	for _, at := range required {
+		if !IsThresholdRequired(at) {
+			t.Errorf("IsThresholdRequired(%q) = false, want true", at)
+		}
+	}
+
+	notRequired := []AlertType{AlertIncomingTx, AlertOutgoingTx}
+	for _, at := range notRequired {
+		if IsThresholdRequired(at) {
+			t.Errorf("IsThresholdRequired(%q) = true, want false", at)
+		}
+	}
+}
--- a/backend-go/internal/handlers/alert_event.go
+++ b/backend-go/internal/handlers/alert_event.go
@@ -4,9 +4,7 @@ import (
 	"log"
 	"net/http"
 	"strconv"
-	"time"

-	"github.com/kjannette/koin-ping/backend-go/internal/domain"
 	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
 	"github.com/kjannette/koin-ping/backend-go/internal/models"
 )
@@ -46,44 +44,5 @@ func (h *AlertEventHandler) List(w http.ResponseWriter, r *http.Request) {

 	log.Printf("Found %d alert events for user", len(events))

-	// MVP scaffolding: return mock data if DB is empty
-	if len(events) == 0 {
-		events = mockEvents(limit)
-	}
-
 	writeJSON(w, http.StatusOK, events)
 }
-
-func mockEvents(limit int) []domain.AlertEvent {
-	label1 := "Treasury Wallet"
-	label2 := "Cold Storage"
-
-	mocks := []domain.AlertEvent{
-		{
-			ID:           1,
-			AlertRuleID:  1,
-			Message:      "Incoming transaction detected: 5.5 ETH received",
-			AddressLabel: &label1,
-			Timestamp:    time.Now().Add(-2 * time.Hour),
-		},
-		{
-			ID:           2,
-			AlertRuleID:  2,
-			Message:      "Balance dropped below threshold: Current balance 8.2 ETH",
-			AddressLabel: &label1,
-			Timestamp:    time.Now().Add(-5 * time.Hour),
-		},
-		{
-			ID:           3,
-			AlertRuleID:  3,
-			Message:      "Outgoing transaction detected: 2.0 ETH sent",
-			AddressLabel: &label2,
-			Timestamp:    time.Now().Add(-24 * time.Hour),
-		},
-	}
-
-	if limit < len(mocks) {
-		return mocks[:limit]
-	}
-	return mocks
-}
--- a/backend-go/internal/handlers/notification_config.go
+++ b/backend-go/internal/handlers/notification_config.go
@@ -10,6 +10,7 @@ import (
 	"github.com/kjannette/koin-ping/backend-go/internal/domain"
 	"github.com/kjannette/koin-ping/backend-go/internal/middleware"
 	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend-go/internal/notifications"
 )

 var emailRe = regexp.MustCompile(`^[^\s@]+@[^\s@]+\.[^\s@]+$`)
@@ -50,7 +51,7 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.

 	var body struct {
 		DiscordWebhookURL   *string `json:"discord_webhook_url"`
-		TelegramChatID      *string `json:"telegram_chat_id"`
+		SlackWebhookURL     *string `json:"slack_webhook_url"`
 		Email               *string `json:"email"`
 		NotificationEnabled *bool   `json:"notification_enabled"`
 	}
@@ -62,7 +63,7 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.

 	log.Printf("User %s updating notification config", userID)

-	if body.DiscordWebhookURL == nil && body.TelegramChatID == nil &&
+	if body.DiscordWebhookURL == nil && body.SlackWebhookURL == nil &&
 		body.Email == nil && body.NotificationEnabled == nil {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
 			"At least one configuration field must be provided")
@@ -76,6 +77,13 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.
 		return
 	}

+	if body.SlackWebhookURL != nil && *body.SlackWebhookURL != "" &&
+		!strings.HasPrefix(*body.SlackWebhookURL, "https://hooks.slack.com/") {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
+			"Invalid Slack webhook URL format")
+		return
+	}
+
 	if body.Email != nil && *body.Email != "" && !emailRe.MatchString(*body.Email) {
 		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR",
 			"Invalid email address format")
@@ -89,7 +97,7 @@ func (h *NotificationConfigHandler) UpdateConfig(w http.ResponseWriter, r *http.

 	cfg := domain.NotificationConfig{
 		DiscordWebhookURL:   body.DiscordWebhookURL,
-		TelegramChatID:      body.TelegramChatID,
+		SlackWebhookURL:     body.SlackWebhookURL,
 		Email:               body.Email,
 		NotificationEnabled: enabled,
 	}
@@ -126,3 +134,50 @@ func (h *NotificationConfigHandler) DeleteConfig(w http.ResponseWriter, r *http.
 	log.Println("Notification config deleted")
 	w.WriteHeader(http.StatusNoContent)
 }
+
+func (h *NotificationConfigHandler) TestWebhook(w http.ResponseWriter, r *http.Request) {
+	_ = middleware.GetUserID(r.Context())
+
+	var body struct {
+		Type string `json:"type"`
+		URL  string `json:"url"`
+	}
+	if err := json.NewDecoder(r.Body).Decode(&body); err != nil {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid request body")
+		return
+	}
+
+	if body.URL == "" {
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "URL is required")
+		return
+	}
+
+	var ok bool
+	var err error
+
+	switch body.Type {
+	case "slack":
+		if !strings.HasPrefix(body.URL, "https://hooks.slack.com/") {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid Slack webhook URL")
+			return
+		}
+		ok, err = notifications.TestSlackWebhook(body.URL)
+	case "discord":
+		if !strings.HasPrefix(body.URL, "https://discord.com/api/webhooks/") {
+			writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Invalid Discord webhook URL")
+			return
+		}
+		ok, err = notifications.TestDiscordWebhook(body.URL)
+	default:
+		writeError(w, http.StatusBadRequest, "VALIDATION_ERROR", "Type must be 'slack' or 'discord'")
+		return
+	}
+
+	if err != nil {
+		log.Printf("Webhook test failed: %v", err)
+		writeJSON(w, http.StatusOK, map[string]interface{}{"success": false, "error": err.Error()})
+		return
+	}
+
+	writeJSON(w, http.StatusOK, map[string]interface{}{"success": ok})
+}
--- a/backend-go/internal/handlers/status.go
+++ b/backend-go/internal/handlers/status.go
@@ -1,8 +1,13 @@
 package handlers

 import (
+	"context"
+	"log"
 	"net/http"
 	"time"
+
+	"github.com/kjannette/koin-ping/backend-go/internal/models"
+	"github.com/kjannette/koin-ping/backend-go/internal/protocols/ethereum"
 )

 func HealthCheck(w http.ResponseWriter, r *http.Request) {
@@ -13,11 +18,62 @@ func HealthCheck(w http.ResponseWriter, r *http.Request) {
 	})
 }

-func SystemStatus(w http.ResponseWriter, r *http.Request) {
+type StatusHandler struct {
+	eth         ethereum.EthereumObserver
+	checkpoints *models.CheckpointModel
+}
+
+func NewStatusHandler(eth ethereum.EthereumObserver, checkpoints *models.CheckpointModel) *StatusHandler {
+	return &StatusHandler{eth: eth, checkpoints: checkpoints}
+}
+
+func (h *StatusHandler) SystemStatus(w http.ResponseWriter, r *http.Request) {
+	ctx, cancel := context.WithTimeout(r.Context(), 10*time.Second)
+	defer cancel()
+
+	status := "healthy"
+
+	if h.eth == nil {
+		writeJSON(w, http.StatusOK, map[string]interface{}{
+			"latestBlock":      0,
+			"lag":              0,
+			"trackedAddresses": 0,
+			"status":           "no_rpc",
+			"timestamp":        time.Now().UTC().Format(time.RFC3339),
+		})
+		return
+	}
+
+	latestBlock, err := h.eth.GetLatestBlockNumber(ctx)
+	if err != nil {
+		log.Printf("Failed to get latest block: %v", err)
+		status = "degraded"
+		latestBlock = 0
+	}
+
+	lag := 0
+	checkpoints, err := h.checkpoints.ListAll(ctx)
+	if err != nil {
+		log.Printf("Failed to list checkpoints: %v", err)
+	} else if len(checkpoints) > 0 && latestBlock > 0 {
+		minChecked := checkpoints[0].LastCheckedBlock
+		for _, cp := range checkpoints[1:] {
+			if cp.LastCheckedBlock < minChecked {
+				minChecked = cp.LastCheckedBlock
+			}
+		}
+		lag = latestBlock - minChecked
+	}
+
+	if lag > 50 {
+		status = "syncing"
+	}
+
 	writeJSON(w, http.StatusOK, map[string]interface{}{
-		"latestBlock": 0,
-		"lag":         0,
-		"status":      "healthy",
-		"timestamp":   time.Now().UTC().Format(time.RFC3339),
+		"latestBlock":      latestBlock,
+		"lag":              lag,
+		"trackedAddresses": len(checkpoints),
+		"status":           status,
+		"timestamp":        time.Now().UTC().Format(time.RFC3339),
 	})
 }
--- a/backend-go/internal/models/notification_config.go
+++ b/backend-go/internal/models/notification_config.go
@@ -18,12 +18,12 @@ func NewNotificationConfigModel(pool *pgxpool.Pool) *NotificationConfigModel {
 func (m *NotificationConfigModel) GetConfig(ctx context.Context, userID string) (*domain.NotificationConfig, error) {
 	var c domain.NotificationConfig
 	err := m.pool.QueryRow(ctx,
-		`SELECT user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
+		`SELECT user_id, discord_webhook_url, slack_webhook_url,
 		        email, notification_enabled, created_at, updated_at
 		 FROM user_notification_configs
 		 WHERE user_id = $1`,
 		userID,
-	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.TelegramBotToken,
+	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.SlackWebhookURL,
 		&c.Email, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
 	if err != nil {
 		if err.Error() == "no rows in result set" {
@@ -38,21 +38,20 @@ func (m *NotificationConfigModel) UpsertConfig(ctx context.Context, userID strin
 	var c domain.NotificationConfig
 	err := m.pool.QueryRow(ctx,
 		`INSERT INTO user_notification_configs
-		   (user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token, email, notification_enabled, updated_at)
-		 VALUES ($1, $2, $3, $4, $5, $6, NOW())
+		   (user_id, discord_webhook_url, slack_webhook_url, email, notification_enabled, updated_at)
+		 VALUES ($1, $2, $3, $4, $5, NOW())
 		 ON CONFLICT (user_id)
 		 DO UPDATE SET
 		   discord_webhook_url = COALESCE($2, user_notification_configs.discord_webhook_url),
-		   telegram_chat_id = COALESCE($3, user_notification_configs.telegram_chat_id),
-		   telegram_bot_token = COALESCE($4, user_notification_configs.telegram_bot_token),
-		   email = COALESCE($5, user_notification_configs.email),
-		   notification_enabled = $6,
+		   slack_webhook_url = COALESCE($3, user_notification_configs.slack_webhook_url),
+		   email = COALESCE($4, user_notification_configs.email),
+		   notification_enabled = $5,
 		   updated_at = NOW()
-		 RETURNING user_id, discord_webhook_url, telegram_chat_id, telegram_bot_token,
+		 RETURNING user_id, discord_webhook_url, slack_webhook_url,
 		           email, notification_enabled, created_at, updated_at`,
-		userID, cfg.DiscordWebhookURL, cfg.TelegramChatID, cfg.TelegramBotToken,
+		userID, cfg.DiscordWebhookURL, cfg.SlackWebhookURL,
 		cfg.Email, cfg.NotificationEnabled,
-	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.TelegramBotToken,
+	).Scan(&c.UserID, &c.DiscordWebhookURL, &c.SlackWebhookURL,
 		&c.Email, &c.NotificationEnabled, &c.CreatedAt, &c.UpdatedAt)
 	if err != nil {
 		return nil, err
@@ -73,7 +72,7 @@ func (m *NotificationConfigModel) Remove(ctx context.Context, userID string) (bo

 func (m *NotificationConfigModel) ListEnabled(ctx context.Context) ([]domain.NotificationConfig, error) {
 	rows, err := m.pool.Query(ctx,
-		`SELECT user_id, discord_webhook_url, telegram_chat_id, email
+		`SELECT user_id, discord_webhook_url, slack_webhook_url, email
 		 FROM user_notification_configs
 		 WHERE notification_enabled = TRUE`,
 	)
@@ -85,7 +84,7 @@ func (m *NotificationConfigModel) ListEnabled(ctx context.Context) ([]domain.Not
 	var configs []domain.NotificationConfig
 	for rows.Next() {
 		var c domain.NotificationConfig
-		if err := rows.Scan(&c.UserID, &c.DiscordWebhookURL, &c.TelegramChatID, &c.Email); err != nil {
+		if err := rows.Scan(&c.UserID, &c.DiscordWebhookURL, &c.SlackWebhookURL, &c.Email); err != nil {
 			return nil, err
 		}
 		c.NotificationEnabled = true
--- a/backend-go/internal/notifications/discord_test.go
+++ b/backend-go/internal/notifications/discord_test.go
@@ -0,0 +1,99 @@
+package notifications
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestSendDiscordNotification(t *testing.T) {
+	var receivedPayload discordPayload
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+
+		body, _ := io.ReadAll(r.Body)
+		json.Unmarshal(body, &receivedPayload)
+
+		w.WriteHeader(http.StatusNoContent)
+	}))
+	defer server.Close()
+
+	meta := AlertMetadata{
+		TxHash:       "0xabc123",
+		AddressLabel: "Treasury",
+		AlertType:    "incoming_tx",
+		Address:      "0x1234567890abcdef1234567890abcdef12345678",
+	}
+
+	sent, err := SendDiscordNotification(server.URL, "Incoming transaction: 5.5 ETH received", meta)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !sent {
+		t.Fatal("expected sent to be true")
+	}
+
+	if len(receivedPayload.Embeds) != 1 {
+		t.Fatalf("expected 1 embed, got %d", len(receivedPayload.Embeds))
+	}
+	embed := receivedPayload.Embeds[0]
+	if embed.Title != "Koin Ping Alert" {
+		t.Errorf("title = %q, want %q", embed.Title, "Koin Ping Alert")
+	}
+	if embed.Color != 0x00ff00 {
+		t.Errorf("color = %x, want %x (green for incoming_tx)", embed.Color, 0x00ff00)
+	}
+	if len(embed.Fields) != 3 {
+		t.Errorf("expected 3 fields (address, blockchain address, tx), got %d", len(embed.Fields))
+	}
+}
+
+func TestSendDiscordNotification_ServerError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusBadRequest)
+	}))
+	defer server.Close()
+
+	sent, err := SendDiscordNotification(server.URL, "test", AlertMetadata{})
+	if err == nil {
+		t.Fatal("expected error for bad response")
+	}
+	if sent {
+		t.Fatal("expected sent to be false")
+	}
+}
+
+func TestTestDiscordWebhook(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusNoContent)
+	}))
+	defer server.Close()
+
+	ok, err := TestDiscordWebhook(server.URL)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !ok {
+		t.Fatal("expected ok to be true")
+	}
+}
+
+func TestColorForAlertType(t *testing.T) {
+	tests := map[string]int{
+		"incoming_tx":    0x00ff00,
+		"outgoing_tx":    0xff9900,
+		"large_transfer": 0xff0000,
+		"balance_below":  0xff0000,
+		"unknown":        0x0099ff,
+	}
+	for alertType, want := range tests {
+		if got := colorForAlertType(alertType); got != want {
+			t.Errorf("colorForAlertType(%q) = %x, want %x", alertType, got, want)
+		}
+	}
+}
--- a/backend-go/internal/notifications/email.go
+++ b/backend-go/internal/notifications/email.go
@@ -0,0 +1,111 @@
+package notifications
+
+import (
+	"fmt"
+	"log"
+	"net/smtp"
+	"strings"
+)
+
+type SMTPConfig struct {
+	Host     string
+	Port     int
+	Username string
+	Password string
+	From     string
+}
+
+func (c *SMTPConfig) IsConfigured() bool {
+	return c.Host != "" && c.From != ""
+}
+
+func (c *SMTPConfig) addr() string {
+	return fmt.Sprintf("%s:%d", c.Host, c.Port)
+}
+
+func SendEmailNotification(cfg SMTPConfig, toEmail, message string, meta AlertMetadata) (bool, error) {
+	if !cfg.IsConfigured() {
+		return false, fmt.Errorf("SMTP is not configured")
+	}
+
+	subject := fmt.Sprintf("Koin Ping Alert: %s", humanAlertType(meta.AlertType))
+
+	body := buildEmailBody(message, meta)
+
+	msg := strings.Join([]string{
+		fmt.Sprintf("From: %s", cfg.From),
+		fmt.Sprintf("To: %s", toEmail),
+		fmt.Sprintf("Subject: %s", subject),
+		"MIME-Version: 1.0",
+		"Content-Type: text/html; charset=UTF-8",
+		"",
+		body,
+	}, "\r\n")
+
+	var auth smtp.Auth
+	if cfg.Username != "" {
+		auth = smtp.PlainAuth("", cfg.Username, cfg.Password, cfg.Host)
+	}
+
+	err := smtp.SendMail(cfg.addr(), auth, cfg.From, []string{toEmail}, []byte(msg))
+	if err != nil {
+		log.Printf("Failed to send email notification to %s: %v", toEmail, err)
+		return false, err
+	}
+
+	return true, nil
+}
+
+func TestEmailNotification(cfg SMTPConfig, toEmail string) (bool, error) {
+	meta := AlertMetadata{AlertType: "test"}
+	return SendEmailNotification(cfg, toEmail,
+		"This is a test notification from Koin Ping. Your email is configured correctly!", meta)
+}
+
+func buildEmailBody(message string, meta AlertMetadata) string {
+	txSection := ""
+	if meta.TxHash != "" {
+		txSection = fmt.Sprintf(
+			`<tr><td style="padding:8px 0;color:#666">Transaction</td>`+
+				`<td style="padding:8px 0"><a href="https://etherscan.io/tx/%s" style="color:#4f46e5">View on Etherscan</a></td></tr>`,
+			meta.TxHash,
+		)
+	}
+
+	return fmt.Sprintf(`<!DOCTYPE html>
+<html>
+<body style="margin:0;padding:0;font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif;background:#f5f5f5">
+  <div style="max-width:560px;margin:24px auto;background:#fff;border-radius:8px;overflow:hidden;box-shadow:0 1px 3px rgba(0,0,0,.1)">
+    <div style="background:#4f46e5;padding:20px 24px">
+      <h1 style="margin:0;color:#fff;font-size:18px">Koin Ping Alert</h1>
+    </div>
+    <div style="padding:24px">
+      <p style="margin:0 0 16px;font-size:15px;color:#333">%s</p>
+      <table style="width:100%%;border-collapse:collapse;font-size:14px">
+        <tr><td style="padding:8px 0;color:#666">Address</td><td style="padding:8px 0">%s</td></tr>
+        <tr><td style="padding:8px 0;color:#666">Blockchain Address</td><td style="padding:8px 0;font-family:monospace;font-size:12px">%s</td></tr>
+        %s
+      </table>
+    </div>
+    <div style="padding:16px 24px;background:#fafafa;font-size:12px;color:#999;text-align:center">
+      Sent by Koin Ping
+    </div>
+  </div>
+</body>
+</html>`, message, meta.AddressLabel, meta.Address, txSection)
+}
+
+func humanAlertType(alertType string) string {
+	switch alertType {
+	case "incoming_tx":
+		return "Incoming Transaction"
+	case "outgoing_tx":
+		return "Outgoing Transaction"
+	case "large_transfer":
+		return "Large Transfer"
+	case "balance_below":
+		return "Balance Below Threshold"
+	default:
+		return "Alert"
+	}
+}
--- a/backend-go/internal/notifications/email_test.go
+++ b/backend-go/internal/notifications/email_test.go
@@ -0,0 +1,102 @@
+package notifications
+
+import (
+	"strings"
+	"testing"
+)
+
+func TestSMTPConfig_IsConfigured(t *testing.T) {
+	tests := []struct {
+		name string
+		cfg  SMTPConfig
+		want bool
+	}{
+		{"fully configured", SMTPConfig{Host: "smtp.example.com", Port: 587, From: "noreply@example.com"}, true},
+		{"missing host", SMTPConfig{Port: 587, From: "noreply@example.com"}, false},
+		{"missing from", SMTPConfig{Host: "smtp.example.com", Port: 587}, false},
+		{"empty", SMTPConfig{}, false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := tt.cfg.IsConfigured(); got != tt.want {
+				t.Errorf("IsConfigured() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestSMTPConfig_Addr(t *testing.T) {
+	cfg := SMTPConfig{Host: "smtp.example.com", Port: 587}
+	if got := cfg.addr(); got != "smtp.example.com:587" {
+		t.Errorf("addr() = %q, want %q", got, "smtp.example.com:587")
+	}
+}
+
+func TestBuildEmailBody(t *testing.T) {
+	meta := AlertMetadata{
+		TxHash:       "0xabc123",
+		AddressLabel: "Treasury",
+		AlertType:    "incoming_tx",
+		Address:      "0x1234567890abcdef1234567890abcdef12345678",
+	}
+
+	body := buildEmailBody("Incoming transaction: 5.5 ETH received", meta)
+
+	if !strings.Contains(body, "Koin Ping Alert") {
+		t.Error("body should contain title")
+	}
+	if !strings.Contains(body, "Incoming transaction: 5.5 ETH received") {
+		t.Error("body should contain message")
+	}
+	if !strings.Contains(body, "Treasury") {
+		t.Error("body should contain address label")
+	}
+	if !strings.Contains(body, "0x1234567890abcdef") {
+		t.Error("body should contain blockchain address")
+	}
+	if !strings.Contains(body, "etherscan.io/tx/0xabc123") {
+		t.Error("body should contain etherscan link")
+	}
+}
+
+func TestBuildEmailBody_NoTxHash(t *testing.T) {
+	meta := AlertMetadata{
+		AddressLabel: "Cold Storage",
+		AlertType:    "balance_below",
+		Address:      "0xabcdef",
+	}
+
+	body := buildEmailBody("Balance dropped below threshold", meta)
+
+	if strings.Contains(body, "etherscan.io") {
+		t.Error("body should not contain etherscan link when no tx hash")
+	}
+}
+
+func TestHumanAlertType(t *testing.T) {
+	tests := map[string]string{
+		"incoming_tx":    "Incoming Transaction",
+		"outgoing_tx":    "Outgoing Transaction",
+		"large_transfer": "Large Transfer",
+		"balance_below":  "Balance Below Threshold",
+		"unknown":        "Alert",
+		"test":           "Alert",
+	}
+	for alertType, want := range tests {
+		if got := humanAlertType(alertType); got != want {
+			t.Errorf("humanAlertType(%q) = %q, want %q", alertType, got, want)
+		}
+	}
+}
+
+func TestSendEmailNotification_NotConfigured(t *testing.T) {
+	cfg := SMTPConfig{}
+	sent, err := SendEmailNotification(cfg, "user@example.com", "test", AlertMetadata{})
+	if err == nil {
+		t.Fatal("expected error for unconfigured SMTP")
+	}
+	if sent {
+		t.Fatal("expected sent to be false")
+	}
+}
--- a/backend-go/internal/notifications/slack.go
+++ b/backend-go/internal/notifications/slack.go
@@ -0,0 +1,128 @@
+package notifications
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"log"
+	"net/http"
+	"time"
+)
+
+type slackBlock struct {
+	Type     string      `json:"type"`
+	Text     *slackText  `json:"text,omitempty"`
+	Fields   []slackText `json:"fields,omitempty"`
+	Elements []slackText `json:"elements,omitempty"`
+}
+
+type slackText struct {
+	Type string `json:"type"`
+	Text string `json:"text"`
+}
+
+type slackPayload struct {
+	Blocks []slackBlock `json:"blocks"`
+}
+
+func SendSlackNotification(webhookURL, message string, meta AlertMetadata) (bool, error) {
+	etherscanLink := ""
+	if meta.TxHash != "" {
+		etherscanLink = fmt.Sprintf("<%s|View on Etherscan>", "https://etherscan.io/tx/"+meta.TxHash)
+	}
+
+	blocks := []slackBlock{
+		{
+			Type: "header",
+			Text: &slackText{Type: "plain_text", Text: emojiForAlertType(meta.AlertType) + " Koin Ping Alert"},
+		},
+		{
+			Type: "section",
+			Text: &slackText{Type: "mrkdwn", Text: message},
+		},
+		{
+			Type: "section",
+			Fields: []slackText{
+				{Type: "mrkdwn", Text: fmt.Sprintf("*Address:*\n%s", meta.AddressLabel)},
+				{Type: "mrkdwn", Text: fmt.Sprintf("*Blockchain Address:*\n`%s`", meta.Address)},
+			},
+		},
+	}
+
+	if etherscanLink != "" {
+		blocks = append(blocks, slackBlock{
+			Type: "section",
+			Text: &slackText{Type: "mrkdwn", Text: fmt.Sprintf("*Transaction:* %s", etherscanLink)},
+		})
+	}
+
+	blocks = append(blocks, slackBlock{
+		Type: "context",
+		Elements: []slackText{
+			{Type: "mrkdwn", Text: fmt.Sprintf("Koin Ping | %s", time.Now().UTC().Format(time.RFC3339))},
+		},
+	})
+
+	payload := slackPayload{Blocks: blocks}
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, fmt.Errorf("marshal slack payload: %w", err)
+	}
+
+	resp, err := http.Post(webhookURL, "application/json", bytes.NewReader(body))
+	if err != nil {
+		log.Printf("Failed to send Slack notification: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	if resp.StatusCode < 200 || resp.StatusCode >= 300 {
+		log.Printf("Slack webhook failed: HTTP %d", resp.StatusCode)
+		return false, fmt.Errorf("slack webhook failed: HTTP %d", resp.StatusCode)
+	}
+
+	return true, nil
+}
+
+func TestSlackWebhook(webhookURL string) (bool, error) {
+	payload := slackPayload{
+		Blocks: []slackBlock{
+			{
+				Type: "section",
+				Text: &slackText{
+					Type: "mrkdwn",
+					Text: "Koin Ping test notification — Your Slack webhook is configured correctly!",
+				},
+			},
+		},
+	}
+
+	body, err := json.Marshal(payload)
+	if err != nil {
+		return false, err
+	}
+
+	resp, err := http.Post(webhookURL, "application/json", bytes.NewReader(body))
+	if err != nil {
+		log.Printf("Slack webhook test failed: %v", err)
+		return false, err
+	}
+	defer resp.Body.Close()
+
+	return resp.StatusCode >= 200 && resp.StatusCode < 300, nil
+}
+
+func emojiForAlertType(alertType string) string {
+	switch alertType {
+	case "incoming_tx":
+		return "📥"
+	case "outgoing_tx":
+		return "📤"
+	case "large_transfer":
+		return "🚨"
+	case "balance_below":
+		return "⚠️"
+	default:
+		return "🔔"
+	}
+}
--- a/backend-go/internal/notifications/slack_test.go
+++ b/backend-go/internal/notifications/slack_test.go
@@ -0,0 +1,128 @@
+package notifications
+
+import (
+	"encoding/json"
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestSendSlackNotification(t *testing.T) {
+	var receivedPayload slackPayload
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.Method != http.MethodPost {
+			t.Errorf("expected POST, got %s", r.Method)
+		}
+		if r.Header.Get("Content-Type") != "application/json" {
+			t.Errorf("expected application/json content type")
+		}
+
+		body, _ := io.ReadAll(r.Body)
+		json.Unmarshal(body, &receivedPayload)
+
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	meta := AlertMetadata{
+		TxHash:       "0xabc123",
+		AddressLabel: "Treasury",
+		AlertType:    "incoming_tx",
+		Address:      "0x1234567890abcdef1234567890abcdef12345678",
+	}
+
+	sent, err := SendSlackNotification(server.URL, "Incoming transaction: 5.5 ETH received", meta)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !sent {
+		t.Fatal("expected sent to be true")
+	}
+
+	if len(receivedPayload.Blocks) < 3 {
+		t.Fatalf("expected at least 3 blocks, got %d", len(receivedPayload.Blocks))
+	}
+	if receivedPayload.Blocks[0].Type != "header" {
+		t.Errorf("first block should be header, got %s", receivedPayload.Blocks[0].Type)
+	}
+}
+
+func TestSendSlackNotification_ServerError(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusInternalServerError)
+	}))
+	defer server.Close()
+
+	sent, err := SendSlackNotification(server.URL, "test", AlertMetadata{})
+	if err == nil {
+		t.Fatal("expected error for server error response")
+	}
+	if sent {
+		t.Fatal("expected sent to be false")
+	}
+}
+
+func TestSendSlackNotification_NoTxHash(t *testing.T) {
+	var receivedPayload slackPayload
+
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		body, _ := io.ReadAll(r.Body)
+		json.Unmarshal(body, &receivedPayload)
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	meta := AlertMetadata{
+		AddressLabel: "Treasury",
+		AlertType:    "balance_below",
+		Address:      "0x1234567890abcdef1234567890abcdef12345678",
+	}
+
+	sent, err := SendSlackNotification(server.URL, "Balance dropped below threshold", meta)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !sent {
+		t.Fatal("expected sent to be true")
+	}
+
+	for _, block := range receivedPayload.Blocks {
+		if block.Text != nil && block.Type == "section" {
+			if block.Text.Text == "*Transaction:*" {
+				t.Error("should not include transaction block when TxHash is empty")
+			}
+		}
+	}
+}
+
+func TestTestSlackWebhook(t *testing.T) {
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusOK)
+	}))
+	defer server.Close()
+
+	ok, err := TestSlackWebhook(server.URL)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if !ok {
+		t.Fatal("expected ok to be true")
+	}
+}
+
+func TestEmojiForAlertType(t *testing.T) {
+	tests := map[string]string{
+		"incoming_tx":    "📥",
+		"outgoing_tx":    "📤",
+		"large_transfer": "🚨",
+		"balance_below":  "⚠️",
+		"unknown":        "🔔",
+	}
+	for alertType, want := range tests {
+		if got := emojiForAlertType(alertType); got != want {
+			t.Errorf("emojiForAlertType(%q) = %q, want %q", alertType, got, want)
+		}
+	}
+}
--- a/backend-go/internal/protocols/ethereum/jsonrpc_test.go
+++ b/backend-go/internal/protocols/ethereum/jsonrpc_test.go
@@ -0,0 +1,96 @@
+package ethereum
+
+import (
+	"math/big"
+	"testing"
+)
+
+func TestHexToInt(t *testing.T) {
+	tests := []struct {
+		hex  string
+		want int
+	}{
+		{"0x0", 0},
+		{"0x1", 1},
+		{"0xa", 10},
+		{"0xff", 255},
+		{"0x100", 256},
+		{"0x1234", 4660},
+	}
+
+	for _, tt := range tests {
+		got, err := hexToInt(tt.hex)
+		if err != nil {
+			t.Fatalf("hexToInt(%q) error: %v", tt.hex, err)
+		}
+		if got != tt.want {
+			t.Errorf("hexToInt(%q) = %d, want %d", tt.hex, got, tt.want)
+		}
+	}
+}
+
+func TestHexToInt_Invalid(t *testing.T) {
+	_, err := hexToInt("xyz")
+	if err == nil {
+		t.Fatal("expected error for invalid hex")
+	}
+}
+
+func TestHexToInt64(t *testing.T) {
+	got, err := hexToInt64("0x5f5e100")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != 100000000 {
+		t.Errorf("got %d, want 100000000", got)
+	}
+}
+
+func TestHexToDecimalString(t *testing.T) {
+	tests := []struct {
+		hex  string
+		want string
+	}{
+		{"0x0", "0"},
+		{"0x", "0"},
+		{"", "0"},
+		{"0x1", "1"},
+		{"0xde0b6b3a7640000", "1000000000000000000"},
+	}
+
+	for _, tt := range tests {
+		got := hexToDecimalString(tt.hex)
+		if got != tt.want {
+			t.Errorf("hexToDecimalString(%q) = %q, want %q", tt.hex, got, tt.want)
+		}
+	}
+}
+
+func TestHexToDecimalString_LargeValues(t *testing.T) {
+	expected := new(big.Int).Mul(
+		big.NewInt(100),
+		new(big.Int).Exp(big.NewInt(10), big.NewInt(18), nil),
+	)
+	hex := "0x" + expected.Text(16)
+	got := hexToDecimalString(hex)
+	if got != expected.String() {
+		t.Errorf("got %q, want %q", got, expected.String())
+	}
+}
+
+func TestNewJsonRpcEthereum_EmptyURL(t *testing.T) {
+	_, err := NewJsonRpcEthereum("")
+	if err == nil {
+		t.Fatal("expected error for empty URL")
+	}
+}
+
+func TestNewJsonRpcEthereum_ValidURL(t *testing.T) {
+	eth, err := NewJsonRpcEthereum("https://example.com/rpc")
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if eth == nil {
+		t.Fatal("expected non-nil client")
+	}
+}
--- a/backend-go/internal/services/evaluator.go
+++ b/backend-go/internal/services/evaluator.go
@@ -18,6 +18,7 @@ type EvaluatorService struct {
 	alertEvents  *models.AlertEventModel
 	addresses    *models.AddressModel
 	notifConfigs *models.NotificationConfigModel
+	smtpConfig   notifications.SMTPConfig
 }

 func NewEvaluatorService(
@@ -26,6 +27,7 @@ func NewEvaluatorService(
 	alertEvents *models.AlertEventModel,
 	addresses *models.AddressModel,
 	notifConfigs *models.NotificationConfigModel,
+	smtpCfg notifications.SMTPConfig,
 ) *EvaluatorService {
 	return &EvaluatorService{
 		eth:          eth,
@@ -33,6 +35,7 @@ func NewEvaluatorService(
 		alertEvents:  alertEvents,
 		addresses:    addresses,
 		notifConfigs: notifConfigs,
+		smtpConfig:   smtpCfg,
 	}
 }

@@ -168,40 +171,56 @@ func (s *EvaluatorService) fireAlert(ctx context.Context, rule domain.AlertRule,

 	log.Printf("[ALERT FIRED] Rule %d (%s) - %s - TX: %s", rule.ID, rule.Type, message, obs.Hash)

-	// Send Discord notification (non-fatal on failure)
 	if addr != nil {
-		go s.sendNotification(ctx, addr.UserID, message, obs, addressLabel, rule, addr.Address)
+		go s.sendNotifications(ctx, addr.UserID, message, obs, addressLabel, rule, addr.Address)
 	}

 	return nil
 }

-func (s *EvaluatorService) sendNotification(ctx context.Context, userID, message string, obs domain.ObservedTx, addressLabel string, rule domain.AlertRule, address string) {
+func (s *EvaluatorService) sendNotifications(ctx context.Context, userID, message string, obs domain.ObservedTx, addressLabel string, rule domain.AlertRule, address string) {
 	notifConfig, err := s.notifConfigs.GetConfig(ctx, userID)
 	if err != nil {
 		log.Printf("Failed to get notification config: %v", err)
 		return
 	}

-	if notifConfig == nil || !notifConfig.NotificationEnabled || notifConfig.DiscordWebhookURL == nil {
+	if notifConfig == nil || !notifConfig.NotificationEnabled {
 		return
 	}

-	sent, err := notifications.SendDiscordNotification(
-		*notifConfig.DiscordWebhookURL,
-		message,
-		notifications.AlertMetadata{
-			TxHash:       obs.Hash,
-			AddressLabel: addressLabel,
-			AlertType:    string(rule.Type),
-			Address:      address,
-		},
-	)
+	meta := notifications.AlertMetadata{
+		TxHash:       obs.Hash,
+		AddressLabel: addressLabel,
+		AlertType:    string(rule.Type),
+		Address:      address,
+	}

-	if err != nil || !sent {
-		log.Printf("Discord notification failed for user %s: %v", userID, err)
-	} else {
-		log.Printf("Discord notification sent to user %s", userID)
+	if notifConfig.DiscordWebhookURL != nil && *notifConfig.DiscordWebhookURL != "" {
+		sent, err := notifications.SendDiscordNotification(*notifConfig.DiscordWebhookURL, message, meta)
+		if err != nil || !sent {
+			log.Printf("Discord notification failed for user %s: %v", userID, err)
+		} else {
+			log.Printf("Discord notification sent to user %s", userID)
+		}
+	}
+
+	if notifConfig.SlackWebhookURL != nil && *notifConfig.SlackWebhookURL != "" {
+		sent, err := notifications.SendSlackNotification(*notifConfig.SlackWebhookURL, message, meta)
+		if err != nil || !sent {
+			log.Printf("Slack notification failed for user %s: %v", userID, err)
+		} else {
+			log.Printf("Slack notification sent to user %s", userID)
+		}
+	}
+
+	if notifConfig.Email != nil && *notifConfig.Email != "" && s.smtpConfig.IsConfigured() {
+		sent, err := notifications.SendEmailNotification(s.smtpConfig, *notifConfig.Email, message, meta)
+		if err != nil || !sent {
+			log.Printf("Email notification failed for user %s: %v", userID, err)
+		} else {
+			log.Printf("Email notification sent to user %s (%s)", userID, *notifConfig.Email)
+		}
 	}
 }

--- a/backend-go/internal/services/observer_test.go
+++ b/backend-go/internal/services/observer_test.go
@@ -0,0 +1,113 @@
+package services
+
+import (
+	"testing"
+
+	"github.com/kjannette/koin-ping/backend-go/internal/domain"
+)
+
+func TestFilterRelevantTransactions(t *testing.T) {
+	to1 := "0xaaaa"
+	to2 := "0xbbbb"
+	to3 := "0xcccc"
+
+	txs := []domain.NormalizedTx{
+		{Hash: "0x1", From: "0xaaaa", To: &to2, Value: "1000"},
+		{Hash: "0x2", From: "0xbbbb", To: &to1, Value: "2000"},
+		{Hash: "0x3", From: "0xcccc", To: &to3, Value: "3000"},
+		{Hash: "0x4", From: "0xdddd", To: nil, Value: "0"},
+	}
+
+	t.Run("finds outgoing", func(t *testing.T) {
+		result := filterRelevantTransactions(txs, "0xAAAA")
+		if len(result) != 2 {
+			t.Fatalf("expected 2 relevant txs (1 from, 1 to), got %d", len(result))
+		}
+	})
+
+	t.Run("finds incoming", func(t *testing.T) {
+		result := filterRelevantTransactions(txs, "0xBBBB")
+		if len(result) != 2 {
+			t.Fatalf("expected 2 relevant txs, got %d", len(result))
+		}
+	})
+
+	t.Run("no match", func(t *testing.T) {
+		result := filterRelevantTransactions(txs, "0x9999")
+		if len(result) != 0 {
+			t.Fatalf("expected 0 relevant txs, got %d", len(result))
+		}
+	})
+
+	t.Run("case insensitive", func(t *testing.T) {
+		result := filterRelevantTransactions(txs, "0xAAAA")
+		if len(result) == 0 {
+			t.Fatal("should match case-insensitively")
+		}
+	})
+}
+
+func TestCreateObservedTx(t *testing.T) {
+	to := "0xaaaa"
+	tx := domain.NormalizedTx{
+		Hash:  "0xhash",
+		From:  "0xbbbb",
+		To:    &to,
+		Value: "1000",
+	}
+
+	t.Run("incoming direction", func(t *testing.T) {
+		addr := domain.Address{ID: 1, Address: "0xaaaa"}
+		obs := createObservedTx(tx, addr)
+		if obs.Direction != domain.DirectionIncoming {
+			t.Errorf("expected incoming, got %s", obs.Direction)
+		}
+		if obs.AddressID != 1 {
+			t.Errorf("expected address ID 1, got %d", obs.AddressID)
+		}
+	})
+
+	t.Run("outgoing direction", func(t *testing.T) {
+		addr := domain.Address{ID: 2, Address: "0xbbbb"}
+		obs := createObservedTx(tx, addr)
+		if obs.Direction != domain.DirectionOutgoing {
+			t.Errorf("expected outgoing, got %s", obs.Direction)
+		}
+	})
+}
+
+func TestGetStartBlock(t *testing.T) {
+	s := &ObserverService{}
+
+	t.Run("no checkpoint uses latest", func(t *testing.T) {
+		got := s.getStartBlock(0, false, 1000)
+		if got != 1000 {
+			t.Errorf("expected 1000, got %d", got)
+		}
+	})
+
+	t.Run("with checkpoint uses next block", func(t *testing.T) {
+		got := s.getStartBlock(999, true, 1000)
+		if got != 1000 {
+			t.Errorf("expected 1000, got %d", got)
+		}
+	})
+}
+
+func TestGetEndBlock(t *testing.T) {
+	s := &ObserverService{}
+
+	t.Run("caps at latest", func(t *testing.T) {
+		got := s.getEndBlock(990, 1000)
+		if got != 1000 {
+			t.Errorf("expected 1000, got %d", got)
+		}
+	})
+
+	t.Run("caps at maxBlocksPerRun", func(t *testing.T) {
+		got := s.getEndBlock(0, 200)
+		if got != maxBlocksPerRun-1 {
+			t.Errorf("expected %d, got %d", maxBlocksPerRun-1, got)
+		}
+	})
+}
--- a/backend-go/internal/wei/converter_test.go
+++ b/backend-go/internal/wei/converter_test.go
@@ -0,0 +1,179 @@
+package wei
+
+import (
+	"math"
+	"testing"
+)
+
+func TestToEth(t *testing.T) {
+	tests := []struct {
+		name    string
+		wei     string
+		want    float64
+		wantErr bool
+	}{
+		{"zero string", "0", 0, false},
+		{"empty string", "", 0, false},
+		{"1 ETH", "1000000000000000000", 1.0, false},
+		{"0.5 ETH", "500000000000000000", 0.5, false},
+		{"10 ETH", "10000000000000000000", 10.0, false},
+		{"small amount", "1000000000000000", 0.001, false},
+		{"1 Wei", "1", 1e-18, false},
+		{"invalid", "notanumber", 0, true},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ToEth(tt.wei)
+			if tt.wantErr {
+				if err == nil {
+					t.Fatal("expected error")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if math.Abs(got-tt.want) > 1e-10 {
+				t.Fatalf("ToEth(%q) = %v, want %v", tt.wei, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestFromEth(t *testing.T) {
+	tests := []struct {
+		name    string
+		eth     float64
+		want    string
+		wantErr bool
+	}{
+		{"zero", 0, "0", false},
+		{"1 ETH", 1.0, "1000000000000000000", false},
+		{"0.5 ETH", 0.5, "500000000000000000", false},
+		{"10 ETH", 10.0, "10000000000000000000", false},
+		{"0.001 ETH", 0.001, "1000000000000000", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := FromEth(tt.eth)
+			if tt.wantErr {
+				if err == nil {
+					t.Fatal("expected error")
+				}
+				return
+			}
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if got != tt.want {
+				t.Fatalf("FromEth(%v) = %q, want %q", tt.eth, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestRoundTrip(t *testing.T) {
+	values := []float64{0.001, 0.1, 1.0, 5.5, 10.0, 100.0}
+	for _, eth := range values {
+		weiStr, err := FromEth(eth)
+		if err != nil {
+			t.Fatalf("FromEth(%v) error: %v", eth, err)
+		}
+		back, err := ToEth(weiStr)
+		if err != nil {
+			t.Fatalf("ToEth(%q) error: %v", weiStr, err)
+		}
+		if math.Abs(back-eth) > 1e-10 {
+			t.Fatalf("round-trip %v → %q → %v (diff: %v)", eth, weiStr, back, back-eth)
+		}
+	}
+}
+
+func TestCompare(t *testing.T) {
+	tests := []struct {
+		name string
+		a, b string
+		want int
+	}{
+		{"equal", "1000", "1000", 0},
+		{"a > b", "2000", "1000", 1},
+		{"a < b", "1000", "2000", -1},
+		{"zero equal", "0", "0", 0},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := Compare(tt.a, tt.b)
+			if err != nil {
+				t.Fatalf("unexpected error: %v", err)
+			}
+			if got != tt.want {
+				t.Fatalf("Compare(%q, %q) = %d, want %d", tt.a, tt.b, got, tt.want)
+			}
+		})
+	}
+}
+
+func TestGreaterThanOrEqual(t *testing.T) {
+	ok, err := GreaterThanOrEqual("2000", "1000")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Fatal("expected true")
+	}
+
+	ok, err = GreaterThanOrEqual("1000", "1000")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Fatal("expected true for equal")
+	}
+
+	ok, err = GreaterThanOrEqual("500", "1000")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ok {
+		t.Fatal("expected false")
+	}
+}
+
+func TestLessThan(t *testing.T) {
+	ok, err := LessThan("500", "1000")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !ok {
+		t.Fatal("expected true")
+	}
+
+	ok, err = LessThan("1000", "1000")
+	if err != nil {
+		t.Fatal(err)
+	}
+	if ok {
+		t.Fatal("expected false for equal")
+	}
+}
+
+func TestFormatAsEth(t *testing.T) {
+	got, err := FormatAsEth("1000000000000000000", 4)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "1.0000 ETH" {
+		t.Fatalf("got %q, want %q", got, "1.0000 ETH")
+	}
+
+	got, err = FormatAsEth("500000000000000000", 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if got != "0.50 ETH" {
+		t.Fatalf("got %q, want %q", got, "0.50 ETH")
+	}
+}