Fixing test_update_field_success_on_retry

[aogier]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [x] Added tests for code changes or test/build only changes
• [x] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

Fixed a document test mock Fixes #431

Approach

Reimplemented a mock so doc.save() gets called during update_field and not mock construction/evaluation. Tests were passing because update_field did not called save() at all, thus making it difficult to spot.

Schema & API Changes

• "No change"

Security and Privacy

• "No change"

Testing

• Modified test_update_field_success_on_retry

Monitoring and Logging

• "No change"

[smithsz]

I'm +1. I think it's pretty clear what that new side_effect def is doing.

The only other thing I can think of doing it mocking the second save with mock.DEFAULT and just asserting there were two calls to .save().

@emlaver what do you reckon?