Unit / widget test: test the NetworkImage or Image.network properties

network_image_test.dart

import 'package:flutter_test/flutter_test.dart';
import 'package:mocktail_image_network/mocktail_image_network.dart';
 
testWidgets(
  'renders an image with the provided image url',
  (tester) async {
    const expectedImageUrl = 'media.giphy.com/example.jpg';
    await mockNetworkImages(() async {
      await tester.pumpWidget(app); // your app is a widget that contains your network image
      /** You should also wrap your NetworkImage or Image.network with a DecoratedBox or other widget as the parent, 
      because finder only finds a "widget", and BoxDecoration/DecorationImage/NetworkImage are NOT a widget.
      Example: 
       app = DecoratedBox(
         decoration: BoxDecoration(
           borderRadius: const BorderRadius.vertical(
             bottom: Radius.circular(8),
           ),
           image: DecorationImage(
             image: NetworkImage(imageUrl),
             fit: BoxFit.cover,
           ),
         ),
       );
      */
    });

    expect(
      find.byWidgetPredicate(
        (Widget widget) =>
            // always start finding from a "widget", then drill down the child until you find your NetworkImage
            widget is DecoratedBox &&
            (((widget.decoration as BoxDecoration).image)?.image
                        as NetworkImage?)
                    ?.url ==
                expectedImageUrl,
      ),
      findsOneWidget,
    );
  },
);