Allow code editors to collect tests

[florentinl]

Motivation

The goal of this PR is to fix calling pytest with --collect-only.
This allows using the vscode python extension to collect, run and debug system-tests.

Changes

• Guard scenario cleanup for --collect-only

• Guard scenario properties for --collect-only (as querying values such as weblog version will fail without running containers)

• Return the number of bytes written when patching the write function for scrubbing (the vscode_pytest plugin inherits this wrapped write function to write to a pipe and relies on this behavior of the original write function)

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

🚀 Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• Anything but tests/ or manifests/ is modified ? I have the approval from R&P team
• A docker base image is modified?
  • the relevant build-XXX-image label is present
• A scenario is added, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

conftest.py                                                             @DataDog/system-tests-core
utils/_context/_scenarios/core.py                                       @DataDog/system-tests-core
utils/_context/core.py                                                  @DataDog/system-tests-core
utils/proxy/scrubber.py                                                 @DataDog/system-tests-core

[cbeauchesne]

A small non blocking comment.

I changed the title, as this PR definitly deserves a change log mention.

TYVM !

[cbeauchesne]

Is this change belongs to this PR ?

[florentinl]

Yes, the vscode extension injects a pytest plugin that inherits the wrapped write and needs its return value. Otherwise the test discovery crashes.