Updates TEST_COVERAGE.md with rules from $push

[alinaliBQ]

Updates TEST_COVERAGE.md with additional coverage rules discovered while writing$push accumulator tests (#257).

Section 1 – Data Type Coverage:

• Added array traversal via field paths (e.g. $a.b on arrays-of-objects) to
the nested structure coverage guidance

Section 2 – Arithmetic Operator Coverage:

• Added rule for testing special float values (NaN, Infinity, -Infinity, -0.0)
mixed with non-numeric types (string, boolean, null, object, array) in
operators that collect or pass through values

Section 15 – Pipeline Stage Coverage:

• Added rule for testing multiple $group stages in a single pipeline, where
each stage performs actual grouping (not just _id: null) and the second re-
aggregates the output of the first

Section 18 – Accumulator Coverage:

• Added Actual Grouping Requirement: accumulator tests must include at least
one multi-group test per test category, not rely exclusively on _id: null
• Added Multiple Accumulators in Single $group: test multiple instances of the
same accumulator in one $group with actual grouping to verify independent
field collection without cross-contamination
• Added Large-Scale Result Verification: prefer verifying actual content over
count-only checks at scale; use loops for expected results and fall back to
server-side content checks ($sum/$min/$max) when full element-by-element
comparison is impractical

[documentdb-triage-tool]

🤖 Auto-triaged by documentdb-triage-tool.

Applied: documentation
Project fields suggested: Component docs · Priority P3 · Effort S · Status In Progress
Confidence: 0.90 (mixed)

Reasoning

component from path globs (docs); effort from diff stats (13+0 LOC, 1 files); LLM: Updates TEST_COVERAGE.md with new rules and guidance discovered during $push accumulator test work — purely a documentation improvement with no code changes.

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