minimal repro

main.dart

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
  
group('Shadows on ShapeDecoration', () {
    Widget build(int elevation) {
      return Center(
        child: RepaintBoundary(
          child: Container(
            margin: const EdgeInsets.all(150.0),
            decoration: ShapeDecoration(
              shape: const BeveledRectangleBorder(borderRadius: BorderRadius.all(Radius.circular(20.0))),
              shadows: kElevationToShadow[elevation],
            ),
            height: 100.0,
            width: 100.0,
          ),
        ),
      );
    }
    for (final int elevation in [1, 2]) {
      testWidgets('elevation $elevation', (WidgetTester tester) async {
        debugDisableShadows = false;
        await tester.pumpWidget(build(elevation));
        await expectLater(
          find.byType(Container),
          matchesGoldenFile('shadow.ShapeDecoration.$elevation.png'),
        );
        debugDisableShadows = true;
      });
    }
  });