failed to take screenshot on flutter web

[linchen2chris]

Failed to take screenshot
Unexpected null value.
dart-sdk/lib/internal/js_dev_runtime/private/ddc_runtime/errors.dart 251:49 throw
dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 528:63 nullCheck
lib/_engine/engine/canvaskit/layer.dart 584:34 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 494:5 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 357:9 preroll
lib/_engine/engine/canvaskit/layer.dart 125:12 prerollChildren
lib/_engine/engine/canvaskit/layer.dart 114:19 preroll
lib/_engine/engine/canvaskit/layer_tree.dart 67:15 flatten
lib/_engine/engine/canvaskit/layer_scene_builder.dart 19:42 toImage
packages/flutter/src/rendering/layer.dart 1282:25 toImage
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter/src/rendering/layer.dart 1266:27 toImage
packages/flutter_gherkin/src/flutter/adapters/widget_tester_app_driver_adapter.dart 89:25 takeScreenshotUsingRenderElement
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter_gherkin/src/flutter/adapters/widget_tester_app_driver_adapter.dart 75:53 takeScreenshotUsingRenderElement
packages/flutter_gherkin/src/flutter/adapters/widget_tester_app_driver_adapter.dart 111:20 screenshot
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter_gherkin/src/flutter/adapters/widget_tester_app_driver_adapter.dart 99:31 screenshot
packages/flutter_gherkin/src/flutter/hooks/attach_screenshot_on_failed_step_hook.dart 26:31 _takeScreenshot
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter_gherkin/src/flutter/hooks/attach_screenshot_on_failed_step_hook.dart 25:33 [_takeScreenshot]
packages/flutter_gherkin/src/flutter/hooks/attach_screenshot_on_failed_step_hook.dart 17:38 onAfterStep
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter_gherkin/src/flutter/hooks/attach_screenshot_on_failed_step_hook.dart 8:27 onAfterStep
packages/gherkin/src/hooks/aggregated_hook.dart 87:28
packages/gherkin/src/hooks/aggregated_hook.dart 94:21 _invokeHooks
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/gherkin/src/hooks/aggregated_hook.dart 89:28 [_invokeHooks]
packages/gherkin/src/hooks/aggregated_hook.dart 87:7 onAfterStep
packages/flutter_gherkin/src/flutter/runners/gherkin_integration_test_runner.dart 478:16 _onAfterStepRun
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter_gherkin/src/flutter/runners/gherkin_integration_test_runner.dart 473:31 [_onAfterStepRun]
packages/flutter_gherkin/src/flutter/runners/gherkin_integration_test_runner.dart 386:11 runStep
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
packages/flutter_gherkin/src/flutter/runners/gherkin_integration_test_runner.dart 321:29 runStep
gherkin_suite_test.g.dart 44:28
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 84:54 runBody
dart-sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart 123:5 _async
gherkin_suite_test.g.dart 42:20
packages/flutter_gherkin/src/flutter/runners/gherkin_integration_test_runner.dart 224:45

[linchen2chris]

flutter: 3.0.5
flutter_gherkin: 3.0.0-rc.17

[jonsamwell]

@linchen2chris are you able to provide a sample which reproduces this?

[linchen2chris]

hi @jonsamwell thanks for your reply, afraid not, it only happen in our huge flutter web app.
the error occurs in 3.0.0rc17 wich screenshot function: takeScreenshotUsingRenderElement

I try 3.0.0rc16 which take screenshot function is

if (kIsWeb) {
      return binding.takeScreenshot(name);
    } else {
      if (Platform.isAndroid) {

and use driver

import 'dart:io';
import 'package:integration_test/integration_test_driver_extended.dart'
    as integration_test_driver;

Future<void> main() => integration_test_driver.integrationDriver(
      onScreenshot: (String screenshotName, List<int> screenshotBytes) async {
        final File image = await File('screenshots/$screenshotName.png')
            .create(recursive: true);
        image.writeAsBytesSync(screenshotBytes);
        return true;
      },
    );

then screenshot images will be generated in screenshot/ folder, but reports has not embeded image data

[linchen2chris]

Hi @jonsamwell the example_with_integration_test also take screenshot in web release mode. takeScreenshotUsingRenderElement only works for debug mode. you could give it a try