Added update tests for setOnInsert

[vic-tsang]

This PR contains:

• update tests for $setOnInsert

Ref:

• issue Add compatibility test for $setOnInsert #399

[documentdb-triage-tool]

🤖 Auto-triaged by documentdb-triage-tool.

Applied: compatibility test, enhancement
Project fields suggested: Component test-coverage · Priority P2 · Effort L · Status Needs Review
Confidence: 0.85 (mixed)

Reasoning

component from path globs (test-coverage, test-framework); effort from diff stats (952+0 LOC, 10 files); LLM: Adds new update operator test cases for $setOnInsert, expanding test coverage for an existing feature.

If a label is wrong, remove it manually and ping @patty-chow so the rules can be tuned. The bot will not re-label items that already have component labels.

[eerxuan]

[Minor] Three open PRs (#566, #570, #576) each create this same file with different contents. Whichever merges first will land its version; the other two will hit merge conflicts and need rebase. Consider coordinating with the authors of #566 and #570 to land one canonical file.

[eerxuan]

[Minor] The case ID and message claim a "null vs missing" distinction, but the assertion only verifies field: None is present — it doesn't actually exercise the missing path. Either rename to preserves_null (drop the "vs missing" framing), or add a sibling test using {$exists: True} filter to prove the field is stored as null and not missing.