Flutter – The following StateError was thrown running a test: Bad state: No element

I’m trying to test a button, but it keeps giving this error

═╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following StateError was thrown running a test:
Bad state: No element

When the exception was thrown, this was the stack:
#0      Iterable.single (dart:core/iterable.dart:670:25)
#1      WidgetController.element (package:flutter_test/src/controller.dart:394:30)
#2      WidgetController.ensureVisible (package:flutter_test/src/controller.dart:1567:73)
#3      main.<anonymous closure> (file:///C:/Users/user/Documents/app/test/widgests/button_test.dart:9:18)
#4      testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:170:29)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

The test description was:
  Test button
════════════════════════════════════════════════════════════════════════════════════════════════════
Test failed. See exception logs above.
The test description was: Test button

✖ Test button

Exited (1)

//file button_test.dart
// ignore_for_file: depend_on_referenced_packages

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('Test button', (tester) async {
    final btnFinder = find.byKey(const Key('button'));
    await tester.ensureVisible(btnFinder);
    await tester.tap(btnFinder);
    await tester.pumpAndSettle();
  });
}

//file button.dart
import 'package:auto_size_text/auto_size_text.dart';
import 'package:flutter/material.dart';

import 'inactivity/universal_tap_handler.dart';

class Button extends StatelessWidget {
  const Button({
    required this.label,
    this.onTap,
    this.icon,
    this.height = 50,
    this.width,
    this.backgroundColor,
    super.key,
  });

  final void Function()? onTap;
  final String label;
  final Widget? icon;
  final double height;
  final double? width;
  final Color? backgroundColor;

  @override
  Widget build(BuildContext context) {

    return SizedBox(
      key: const Key('button'),
      height: height,
      width: width ?? double.infinity,
      child: Card(
        elevation: 5,
        color: const Color(0xFFC2A79F),
        margin: const EdgeInsets.all(0),
        child: UniversalTapHandler(
          onTap: onTap!,
          child: Row(
            children: [
              // Label
              Expanded(
                child: Center(
                  child: AutoSizeText(
                    label.toUpperCase(),
                    maxLines: 1,
                    textAlign: TextAlign.left,
                    style: const TextStyle(
                      fontSize: 16,
                      color: Color(0xFFEDE0D2),
                      fontWeight: FontWeight.w800,
                    ),
                  ),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}

    // file UniversalTapHandler
    class UniversalTapHandler extends RawGestureDetector {
  UniversalTapHandler({
    required GestureTapCallback onTap,
    required Widget child,
    super.key,
  }) : super(
          gestures: <Type, GestureRecognizerFactory>{
            _UniversalPointerHandler: GestureRecognizerFactoryWithHandlers<_UniversalPointerHandler>(
              () => _UniversalPointerHandler(),
              (instance) {
                instance.onTap = onTap;
              },
            ),
          },
          child: child,
        );
}

class _UniversalPointerHandler extends TapGestureRecognizer {
  @override
  void rejectGesture(int pointer) {
    acceptGesture(pointer);
  }
}