Migrate empty `Struct`s to `Opaque`
diff --git a/test/number_format_compact_icu_test.dart b/test/number_format_compact_icu_test.dart
index cca7e08..09254c3 100644
--- a/test/number_format_compact_icu_test.dart
+++ b/test/number_format_compact_icu_test.dart
@@ -229,10 +229,10 @@
typedef UErrorNameOp = Pointer<Utf8> Function(int code);
/// [UNumberFormatter](http://icu-project.org/apiref/icu4c/unumberformatter_8h.html#a7c1238b2dd08f32f1ea245ece41e71bd)
-class UNumberFormatter extends Struct {}
+class UNumberFormatter extends Opaque {}
/// [UFormattedNumber](http://icu-project.org/apiref/icu4c/unumberformatter_8h.html#a9d4030bdc4dd1ec4de828bf1bcf4b1b6)
-class UFormattedNumber extends Struct {}
+class UFormattedNumber extends Opaque {}
/// C signature for
/// [unumf_openForSkeletonAndLocale()](http://icu-project.org/apiref/icu4c/unumberformatter_8h.html#a29339e144833880bda36fb7c17032698)
