[pigeon] cleaned up run_test.sh

[gaaclarke]

changes:

• added ability to specify what class of test you want to run
• added list of available tests
• stages are all refactored into functions
• dart compilation tests run on null-safe and non-null-safe now (in parallel)
• removed -x added some print statements
• moved to bash
• made variables all lowercase to avoid collisions

Pre-launch Checklist

• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [shared_preferences]
• 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 Flutter Style Guide.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt.
• I updated pubspec.yaml with an appropriate new version according to the pub versioning philosophy.
• I updated CHANGELOG.md to add a description of the change.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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[xster]

what's ./e2e_tests/test_objc/.packages about? Add a comment?

[gaaclarke]

Commented, I could probably make flutter a dev dependency for pigeon as an alternative.

[xster]

why the dartfmt here?

[gaaclarke]

Those files can be checked in. I'm still on the fence of if thats a good idea. In my PR's I never check them in, but external contributors always do and it makes it easier to review their changes.

[xster]

do we also need to add a warning somewhere saying if you add more tests, you must list them here?

[gaaclarke]

I don't think so. When doing TDD you'll add the tests here as you implement them for the different generators.

[xster]

what's the significance of e2e_tests/test_objc/ in the java test? If there's a special pigeon schema file in that test, should it be moved somewhere more generic?

[gaaclarke]

It's for the aforementioned hack to get access to Flutter. Added comment

[xster]

seems like this one test is different than the rest? Should it be called something more special?

Not clear to me whether this is a unit test against the pigeon tool implementation itself (i.e. unit tests the ast.dart etc) or it's a unit test against the pigeon schema file.

[gaaclarke]

reworded