Organize backend into product executable and shared Go modules

backend/shared/logging/mask/mask_test.go

@@ -0,0 +1,21 @@
+package mask
+
+import (
+	"reflect"
+	"testing"
+)
+
+func TestEmailsMasksEachEmail(t *testing.T) {
+	got := Emails([]string{"alice@example.com", "bo@example.org", "invalid"})
+	want := []string{"a***e@example.com", "b***@example.org", "invalid"}
+
+	if !reflect.DeepEqual(got, want) {
+		t.Fatalf("Emails() = %#v, want %#v", got, want)
+	}
+}
+
+func TestEmailsPreservesNil(t *testing.T) {
+	if got := Emails(nil); got != nil {
+		t.Fatalf("Emails(nil) = %#v, want nil", got)
+	}
+}