[flutter_markdown] add AssetManifest.bin to TestAssetBundle

[andrewkolos]

See #3420 (comment). Fixes a test broken by flutter/flutter#121322.

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the relevant style guides and ran the auto-formatter. (Unlike the flutter/flutter repo, the flutter/packages repo does use dart format.)
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• I listed at least one issue that this PR fixes in the description above.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy, or this PR is exempt from version changes.
• I updated CHANGELOG.md to add a description of the change, following repository CHANGELOG style.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is test-exempt.
• All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel on Discord.

[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 Hixie on the #hackers channel in Chat (don't just cc him here, he won't see it! He's on 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.

[cyanglaz]

LGTM

[stuartmorgan-g]

No version/changelog needed: dev_dependencies changes are dev-only.

[andrewkolos]

I'm afraid to merge since running flutter test against flutter_markdown locally results in some golden test failures with a 0.00% diff. Does this not mean the compared images are identical--or am I misinterpreting?

flutter test output

00:04 +167: /Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/image_test.dart: Image should work with resources                                                                                                                              
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown while running async test code:
Golden "assets/images/golden/image_test/resource_asset_logo.png": Pixel test failed, 0.00% diff
detected.
Failure feedback can be found at
/Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/failures

When the exception was thrown, this was the stack:
#0      LocalFileComparator.compare (package:flutter_test/src/_goldens_io.dart:101:7)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

The exception was caught asynchronously.
════════════════════════════════════════════════════════════════════════════════════════════════════
00:04 +167 -1: /Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/image_test.dart: Image should work with resources [E]                                                                                                                       
  Test failed. See exception logs above.
  The test description was: should work with resources
  

To run this test again: /Users/andrewkolos/Documents/GitHub/flutter/bin/cache/dart-sdk/bin/dart test /Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/image_test.dart -p vm --plain-name 'Image should work with resources'
00:05 +239 ~1 -1: /Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/image_test.dart: Image custom image builder                                                                                                                              
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following assertion was thrown while running async test code:
Golden "assets/images/golden/image_test/custom_builder_asset_logo.png": Pixel test failed, 0.00%
diff detected.
Failure feedback can be found at
/Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/failures

When the exception was thrown, this was the stack:
#0      LocalFileComparator.compare (package:flutter_test/src/_goldens_io.dart:101:7)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

The exception was caught asynchronously.
════════════════════════════════════════════════════════════════════════════════════════════════════
00:05 +239 ~1 -2: /Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/image_test.dart: Image custom image builder [E]                                                                                                                          
  Test failed. See exception logs above.
  The test description was: custom image builder
  

To run this test again: /Users/andrewkolos/Documents/GitHub/flutter/bin/cache/dart-sdk/bin/dart test /Users/andrewkolos/Documents/GitHub/blendthink/packages/packages/flutter_markdown/test/image_test.dart -p vm --plain-name 'Image custom image builder'
00:05 +318 ~4 -2: Some tests failed.  

[jonahwilliams]

goldens are only valid on the machine they were generated on, more or less. I wouldn't worry about it