Add a throw statement for imgtestAdd non 0 exit codes.

[matanlurey]

Thanks @Piinks for noticing.

[flutter-dashboard]

It looks like this pull request may not have tests. Please make sure to add tests before merging. If you need an exemption to this rule, contact "@test-exemption-reviewer" in the #hackers channel in Chat (don't just cc them here, they won't see it! Use Discord!).

If you are not sure if you need tests, consider this rule of thumb: the purpose of a test is to make sure someone doesn't accidentally revert the fix. Ask yourself, is there anything in your PR that you feel it is important we not accidentally revert back to how it was before your fix?

Reviewers: Read the Tree Hygiene page and make sure this patch meets those guidelines before LGTMing.

[mdebbar]

LGTM and thanks @Piinks for catching this!

[Piinks]

Still unclear why this is untested?

[Piinks]

Gonna nit this error message to try to encourage consistency across flutter/flutter and flutter/engine. In the framework we provide links to the dashboard for triage etc.

[Piinks]

This is where we handle this case in the framework: https://github.com/flutter/flutter/blob/b09a015ff5677da6cd9bb631ca44b801953cb2ad/packages/flutter_goldens/lib/skia_client.dart#L237

[Piinks]

So here it would be (I think the result-state.json file is not necessary):

final StringBuffer buf = StringBuffer()
        ..writeln('Skia Gold received an unapproved image in post-submit ')
        ..writeln('testing. Golden file images in flutter/engine are triaged ')
        ..writeln('in pre-submit during code review for the given PR.')
        ..writeln()
        ..writeln('Visit https://flutter-engine-gold.skia.org/ to view and approve ')
        ..writeln('the image(s), or revert the associated change. For more ')
        ..writeln('information, visit the wiki: ')
        ..writeln('https://github.com/flutter/flutter/wiki/Writing-a-golden-file-test-for-package:flutter')
        ..writeln()
        ..writeln('Debug information for Gold --------------------------------')
        ..writeln('stdout: ${result.stdout}')
        ..writeln('stderr: ${result.stderr}');
      throw SkiaException(buf.toString());

[matanlurey]

Nit appreciated and updated.

[matanlurey]

Still unclear why this is untested?

It's untested because it was allowed to be submitted without tests 😅 .

I can volunteer to write some tests, but it won't be in the same PR.