App Screenshots

In-App Screenshots

Produces PNGs of a widget or flow rendered inside the real app shell, at phone and desktop viewports, with real fonts and icons. It runs through flutter test --update-goldens — fully offline and deterministic — so it does not require a display, the GUI app, or driving the device.

This is a visualization tool, not a golden test: there are no committed reference images. You write a throwaway capture test, emit the PNGs, share them, then delete the test. Nothing screenshot-related gets committed unless the user explicitly asks to keep it.

When to use

• "Show me the <screen/modal/dialog> in app context."
• "What does this change look like on mobile vs desktop?"
• Previewing a UI change for design review.

For "is this change actually wired up / does it behave correctly", prefer the verify skill (runs the real app). This skill is about appearance.

The harness

test/test_utils/screenshot_harness.dart provides:

• loadAppFonts() — loads every bundled font (app families + Material/Cupertino icon fonts + icon-font packages) from FontManifest.json. Call once in setUpAll. Without it, glyphs and icons render as boxes.
• screenshotTheme({bool dark = true}) — the production withOverrides theme with Inter applied to the Material text themes (the bare test theme falls back to an unbundled font otherwise).
• captureInApp(tester, {child, name, size, dark, devicePixelRatio, overrides, interaction, outputDir}) — sizes the view, pumps child in the app shell, runs interaction (open a modal, tap a FAB, focus a field…), then writes <outputDir>/<name>.png relative to the calling test file's directory.
• ScreenshotViewport.phone (390×844) and ScreenshotViewport.desktop (1280×800).

Workflow

1. Find the surface and how to reach the state. Identify the entry widget (often a tab/page like ProjectsTabPage) and the tap/scroll needed to reach the state to capture (e.g. tapping the FAB to open a modal). Reuse existing widget tests for that surface to learn the required service registrations and provider overrides — copy their setUp.

2. Write a throwaway capture test at test/_scratch_capture_test.dart (the _scratch_ prefix marks it disposable). Use setUpTestGetIt + additionalSetup for services the surface resolves through getIt, and pass provider overrides via captureInApp(overrides: ...). Drive the state in interaction.

3. Generate the PNGs:

   fvm flutter test --update-goldens test/_scratch_capture_test.dart
   

   Images land in test/screenshots/ (the outputDir, next to the test).

4. View and share. Read the PNGs to inspect them; send them to the user with SendUserFile.

5. Clean up — this is mandatory unless the user asks to keep anything:

   rm test/_scratch_capture_test.dart && rm -rf test/screenshots
   

Example capture test

import 'package:flutter/material.dart';
import 'package:flutter_riverpod/flutter_riverpod.dart';
import 'package:flutter_riverpod/misc.dart'; // Override
import 'package:flutter_test/flutter_test.dart';
import 'package:lotti/classes/project_data.dart';
import 'package:lotti/features/projects/model/projects_overview_models.dart';
import 'package:lotti/features/projects/state/project_providers.dart';
import 'package:lotti/features/projects/ui/pages/projects_tab_page.dart';
import 'package:lotti/features/user_activity/state/user_activity_service.dart';
import 'package:lotti/get_it.dart';
import 'package:lotti/services/entities_cache_service.dart';
import 'package:lotti/services/nav_service.dart';
import 'package:mocktail/mocktail.dart';

import 'features/categories/test_utils.dart';
import 'features/projects/test_utils.dart';
import 'mocks/mocks.dart';
import 'test_utils/screenshot_harness.dart';
import 'widget_test_utils.dart';

void main() {
  setUpAll(loadAppFonts);

  final groups = [
    ProjectCategoryGroup(
      categoryId: 'lotti',
      category: CategoryTestUtils.createTestCategory(id: 'lotti', name: 'Lotti'),
      projects: [
        ProjectListItemData(
          project: makeTestProject(id: 'p1', title: 'Daily Operating System'),
          category: CategoryTestUtils.createTestCategory(id: 'lotti', name: 'Lotti'),
          taskRollup: const ProjectTaskRollupData(totalTaskCount: 25),
        ),
      ],
    ),
  ];

  List<Override> overrides() => [
    projectsOverviewProvider.overrideWith(
      (ref) => Stream.value(ProjectsOverviewSnapshot(groups: groups)),
    ),
    visibleProjectGroupsProvider.overrideWith((ref) => AsyncValue.data(groups)),
  ];

  setUp(() async {
    await setUpTestGetIt(
      additionalSetup: () {
        final activity = MockUserActivityService();
        when(activity.updateActivity).thenReturn(null);
        getIt.registerSingleton<UserActivityService>(activity);

        final nav = MockNavService();
        when(() => nav.isDesktopMode).thenReturn(false);
        when(() => nav.desktopSelectedProjectId)
            .thenReturn(ValueNotifier<String?>(null));
        getIt.registerSingleton<NavService>(nav);

        final cache = MockEntitiesCacheService();
        when(() => cache.getCategoryById(any())).thenReturn(null);
        getIt.registerSingleton<EntitiesCacheService>(cache);
      },
    );
  });
  tearDown(tearDownTestGetIt);

  Future<void> openCreate(WidgetTester tester) =>
      tester.tap(find.bySemanticsLabel('New Project'));

  testWidgets('phone', (tester) async {
    await captureInApp(
      tester,
      child: const ProjectsTabPage(),
      name: 'create_mobile',
      overrides: overrides(),
      interaction: openCreate,
    );
  });

  testWidgets('desktop', (tester) async {
    await captureInApp(
      tester,
      child: const ProjectsTabPage(),
      name: 'create_desktop',
      size: ScreenshotViewport.desktop,
      overrides: overrides(),
      interaction: openCreate,
    );
  });
}

Gotchas

• Override lives in package:flutter_riverpod/misc.dart in this Riverpod version — import it for the List<Override> type (separate from flutter_riverpod.dart, which has AsyncValue).
• Register every service the surface touches via setUpTestGetIt's additionalSetup, or the widget throws on a missing getIt registration. Modals pull in their own deps (e.g. the create modal's CategoryField needs EntitiesCacheService).
• Desktop layout is width-driven. captureInApp(size: ScreenshotViewport.desktop) sets both the view physical size and MediaQuery, so width-gated split views (isDesktopLayout) and the dialog branch (modal page breakpoint) engage correctly.
• Capture target is find.byType(MaterialApp) so overlay content (modals, dialogs, toasts) is included, not just the page body.
• Don't commit the scratch test or test/screenshots/. Delete them when done. The harness itself is the only permanent artifact.