Standardise Python to language agnostic errors

[kieran-ryan]

🤔 What's changed?

• Consolidate Python error messages to standardised format

<TBD>

⚡️ What's your motivation?

• Closes Python: Make tests pass against shared test data #18

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

♻️ Anything particular you want feedback on?

• At present, it appears this will affect some unit tests within behave matching these error messages - with behave pinning cucumber-tag-expressions >= 4.1.0
• Whether consider any regressions within error messages
• Whether appropriate to align these errors with other implementations - given the reason listed against the error messages: "TOO MANY DIFFERENCES: Error message here are more specific (IMHO)"
• Guidance/direction - what is appropriate way to resolve - interested in all perspectives
• Points of extension within Behave - for awareness

📋 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.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[kieran-ryan]

Pending small optimisations following redactions, some further exploratory testing, cleaning up the PR description; properly evaluating compatibility with points of extension by Behave; and ultimately agreement on whether aligning with this format is something we should proceed with (particularly if any error messages considered a regression) or whether we should look to enhance messages (or even a subset) alongside.

[luke-hill]

Hi @kieran-ryan

As mentioned on the issue. We should first get the existing tests fully ran and passing for python. Then we should look to see the new exploratory PR running for python.

So lets get this PR ready to merge, merge it and we'll cut a version that has python running against the same suite as everyone else and move on from there