Add exception to TestStepFinished TestRunFinished

[mpkorstanje]

🤔 What's changed?

To implement a message based JUnit XML Formatter (cucumber/junit-xml-formatter#3) we need to know the class and message of the exception that caused the scenario to fail. This information is often included implicitly in the message field but can not be reliably extracted.

For example if a scenario failed duo to a assertion exception the failure should be rendered as:

<failure message="[The scenario has pending or undefined step(s)](expected: <\"a\"> but was: <\"b\">)" type="org.opentest4j.AssertionFailedError">
  <![CDATA[

... Detailed stack trace here

]]>
</failure>

Currently however we can only render the stack trace part. The other information is not available.

🏷️ What kind of change is this?

• ⚡ New feature (non-breaking change which adds new behaviour)

♻️ Anything particular you want feedback on?

Is this generic enough to work in other languages?

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[davidjgoss]

Is this generic enough to work in other languages?

I think it's okay at least from a JS persective. We can always provide a generic fallback if those fields are not present?

You mentioned the flatness of the structure before, I guess the alternative would be an exception sub-object with type and message fields - this would then be a natural place for additional granular detail about the exception to go e.g. actual vs expected when we eventually get to that.

[mpkorstanje]

Good one. There are some proposals to add more information about exceptions.

• Add more info alongside failed steps in messages to inform about the failure itself #70
• Supply expected / actual in separate fields #69

[mpkorstanje]

I've added an Exception object with type and message fields. I looked at adding stacktrace and expected and actual but it's a bit too much work to see that every language can do with stack traces.

[davidjgoss]

What's the use case for the exception on TestRunFinished out of interest?

[mpkorstanje]

To inform about exceptions that didn't happen in steps or global hooks. For example in Cucumber JVM this would be related to creating the dependency injection container.

Cucumbers execution model can be seen as a tree of containers. Each container has a started and finished event. Each finished event should have an exception for exceptions that occurred in that container.