SFN: Allow ProgramError without details

[bblommers]

Motivation

Bugfix in how SFN handles an ErrorState without any details.

Testing

Example template that I've used to verify this works against AWS:

{
  "StartAt": "ChoiceStateX",
  "States": {
    "ChoiceStateX": {
      "Type": "Choice",
      "Choices": [
        {
          "And": [{"Variable": "$.type", "StringEquals": "Public"}],
          "Next": "Public"
        }
      ],
      "Default": "DefaultState"
    },
    "Public": {"Type": "Pass", "End": true},
    "DefaultState": {
      "Type": "Fail"
    }
  }
}

Note the DefaultState at the end; it does not have an error or cause, and AWS will accept this (and simply return 'cause': None, 'error': None)

StackTrace

This is what it looks like without these fixes:

Traceback (most recent call last):
    File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
      self.run()
    File "/usr/lib/python3.10/threading.py", line 953, in run
      self._target(*self._args, **self._kwargs)
    File "/.../stepfunctions/backend/execution_worker.py", line 76, in _execution_logic
      self._exec_comm.terminated()
    File "/.../stepfunctions/backend/execution.py", line 68, in terminated
      self.execution.error = exit_program_state.error["error"]
  KeyError: 'error'
  
    warnings.warn(pytest.PytestUnhandledThreadExceptionWarning(msg))

[localstack-bot]

Welcome to LocalStack! Thanks for raising your first Pull Request and landing in your contributions. Our team will reach out with any reviews or feedbacks that we have shortly. We recommend joining our Slack Community and share your PR on the #community channel to share your contributions with us. Please make sure you are following our contributing guidelines and our Code of Conduct.

[localstack-bot]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[bblommers]

I have read the CLA Document and I hereby sign the CLA

[coveralls]

coverage: 83.469% (-2.4%) from 85.885%
when pulling af00016 on bblommers-patch-1
into cc55cb4 on master.

[github-actions]

LocalStack Community integration with Pro

    2 files      2 suites   1h 24m 56s ⏱️
2 691 tests 2 435 ✅ 256 💤 0 ❌
2 693 runs  2 435 ✅ 258 💤 0 ❌

Results for commit af00016.

♻️ This comment has been updated with latest results.

[MEPalma]

Thank you @bblommers! Could we please have a snapshot test for this scenario

[bblommers]

Hi @MEPalma! There is a test for this exact scenario, actually, so I decided to just extend the test to also capture the describe_execution call, as that is the operation that showcases the problem.

Let me know if you're OK with this approach - this change seemed the least invasive to me.

[MEPalma]

Thanks again!