welcome message: link @zio with a mention entity

internal/domain/welcome_message_test.go

@@ -0,0 +1,29 @@
+package domain
+
+import (
+	"testing"
+	"unicode/utf16"
+)
+
+func TestOfficialWelcomeMessageLinksUpdatesChannel(t *testing.T) {
+	for _, method := range []string{"phone number", "email"} {
+		msg, err := OfficialWelcomeMessage(1780243200, method, 1_700_000_000)
+		if err != nil {
+			t.Fatalf("method %q: %v", method, err)
+		}
+		if len(msg.Entities) != 1 {
+			t.Fatalf("method %q: entities = %+v, want one mention", method, msg.Entities)
+		}
+		ent := msg.Entities[0]
+		if ent.Type != MessageEntityMention {
+			t.Fatalf("entity type = %q, want mention", ent.Type)
+		}
+		units := utf16.Encode([]rune(msg.Body))
+		if ent.Offset < 0 || ent.Length <= 0 || ent.Offset+ent.Length > len(units) {
+			t.Fatalf("entity %+v out of bounds for body of %d utf16 units", ent, len(units))
+		}
+		if got := string(utf16.Decode(units[ent.Offset : ent.Offset+ent.Length])); got != officialUpdatesChannelMention {
+			t.Fatalf("entity spans %q, want %q", got, officialUpdatesChannelMention)
+		}
+	}
+}