diff --git a/db/store_test.go b/db/store_test.go
new file mode 100644
index 0000000..125711c
--- /dev/null
+++ b/db/store_test.go
@@ -0,0 +1,88 @@
+package db
+
+import (
+	"testing"
+	"time"
+
+	"github.com/google/uuid"
+	"github.com/jackc/pgx/v5/pgtype"
+)
+
+func TestNullableUUID_Zero(t *testing.T) {
+	if nullableUUID(uuid.UUID{}) != nil {
+		t.Error("expected nil for zero UUID")
+	}
+}
+
+func TestNullableUUID_NonZero(t *testing.T) {
+	id := uuid.New()
+	result := nullableUUID(id)
+	if result == nil {
+		t.Fatal("expected non-nil for non-zero UUID")
+	}
+	if *result != id {
+		t.Errorf("expected %s, got %s", id, *result)
+	}
+}
+
+func TestTristate_Nil(t *testing.T) {
+	if tristate(nil) != "any" {
+		t.Error("expected \"any\" for nil")
+	}
+}
+
+func TestTristate_True(t *testing.T) {
+	b := true
+	if tristate(&b) != "true" {
+		t.Error("expected \"true\" for true")
+	}
+}
+
+func TestTristate_False(t *testing.T) {
+	b := false
+	if tristate(&b) != "false" {
+		t.Error("expected \"false\" for false")
+	}
+}
+
+func TestToChannelMessage(t *testing.T) {
+	senderName := "Alice"
+	content := "hello"
+	channelHash := []byte{0xab}
+	sentAt := pgtype.Timestamptz{Time: time.UnixMilli(1700000000000), Valid: true}
+
+	msg := toChannelMessage(42, "deadbeef", channelHash, &senderName, &content, sentAt, 7)
+
+	if msg.ID != 42 {
+		t.Errorf("expected ID 42, got %d", msg.ID)
+	}
+	if msg.PacketHash != "deadbeef" {
+		t.Errorf("expected PacketHash deadbeef, got %s", msg.PacketHash)
+	}
+	if msg.ChannelHash != "ab" {
+		t.Errorf("expected ChannelHash ab, got %s", msg.ChannelHash)
+	}
+	if msg.SenderName != "Alice" {
+		t.Errorf("expected SenderName Alice, got %s", msg.SenderName)
+	}
+	if msg.Content != "hello" {
+		t.Errorf("expected Content hello, got %s", msg.Content)
+	}
+	if msg.SentAt != 1700000000000 {
+		t.Errorf("expected SentAt 1700000000000, got %d", msg.SentAt)
+	}
+	if msg.ObservationCount != 7 {
+		t.Errorf("expected ObservationCount 7, got %d", msg.ObservationCount)
+	}
+}
+
+func TestToChannelMessage_NilFields(t *testing.T) {
+	sentAt := pgtype.Timestamptz{Time: time.UnixMilli(0), Valid: true}
+	msg := toChannelMessage(1, "abc", []byte{0x01}, nil, nil, sentAt, 0)
+	if msg.SenderName != "" {
+		t.Errorf("expected empty SenderName, got %s", msg.SenderName)
+	}
+	if msg.Content != "" {
+		t.Errorf("expected empty Content, got %s", msg.Content)
+	}
+}