docs(test): require production-reachable unit tests

[thieman]

Had the clanker try to self-remediate based on this discussion around some useless tests #2185 (comment)

Summary

• Require unit tests to exercise a production behavior or branch.
• Prohibit tests whose sole subject is a test-only helper.
• Add a counterfactual self-review check based on mutating or removing the claimed production behavior.

Motivation

A review of test-only networking helpers in #2185 showed that realistic setup and strong-looking assertions can still provide no production coverage. These rules make production reachability and mutation sensitivity explicit review requirements.

Test plan

• make check-docs
• Repository pre-commit checks

[pr-commenter]

Binary Size Analysis (Agent Data Plane)

Baseline: f90357b · Comparison: 11a3ac3 · diff
Analysis Configuration: stripped binaries · Pass/Fail Threshold: +5%
Sizes: 40.83 MiB (baseline) vs 40.83 MiB (comparison)
Size Change: -8 B (-0.00%)

✅ Binary size difference within threshold

Changes by Module

Module	File Size	Symbols
anon.44a0faa3240fa409baa379409d152aec.1.llvm.12655547928165574868	-130 B	1
anon.44a0faa3240fa409baa379409d152aec.1.llvm.8379627709259428528	+129 B	1
anon.44a0faa3240fa409baa379409d152aec.4.llvm.12655547928165574868	-114 B	1
anon.44a0faa3240fa409baa379409d152aec.4.llvm.8379627709259428528	+113 B	1
anon.44a0faa3240fa409baa379409d152aec.3.llvm.12655547928165574868	-109 B	1
anon.44a0faa3240fa409baa379409d152aec.3.llvm.8379627709259428528	+108 B	1
anon.44a0faa3240fa409baa379409d152aec.0.llvm.12655547928165574868	-97 B	1
anon.44a0faa3240fa409baa379409d152aec.0.llvm.8379627709259428528	+96 B	1
anon.44a0faa3240fa409baa379409d152aec.2.llvm.12655547928165574868	-95 B	1
anon.44a0faa3240fa409baa379409d152aec.2.llvm.8379627709259428528	+94 B	1
[Unmapped]	-3 B	1

Detailed Symbol Changes

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  [NEW]    +129  [NEW]     +40    anon.44a0faa3240fa409baa379409d152aec.1.llvm.8379627709259428528
  [NEW]    +113  [NEW]     +24    anon.44a0faa3240fa409baa379409d152aec.4.llvm.8379627709259428528
  [NEW]    +108  [NEW]     +19    anon.44a0faa3240fa409baa379409d152aec.3.llvm.8379627709259428528
  [NEW]     +96  [NEW]      +7    anon.44a0faa3240fa409baa379409d152aec.0.llvm.8379627709259428528
  [NEW]     +94  [NEW]      +5    anon.44a0faa3240fa409baa379409d152aec.2.llvm.8379627709259428528
  -5.0%      -3  [ = ]       0    [Unmapped]
  [DEL]     -95  [DEL]      -5    anon.44a0faa3240fa409baa379409d152aec.2.llvm.12655547928165574868
  [DEL]     -97  [DEL]      -7    anon.44a0faa3240fa409baa379409d152aec.0.llvm.12655547928165574868
  [DEL]    -109  [DEL]     -19    anon.44a0faa3240fa409baa379409d152aec.3.llvm.12655547928165574868
  [DEL]    -114  [DEL]     -24    anon.44a0faa3240fa409baa379409d152aec.4.llvm.12655547928165574868
  [DEL]    -130  [DEL]     -40    anon.44a0faa3240fa409baa379409d152aec.1.llvm.12655547928165574868
  -0.0%      -8  [ = ]       0    TOTAL

[datadog-official]

More details

The PR adds documentation-only review guidance requiring tests to reach production behavior and survive a counterfactual mutation. The wording is consistent with the surrounding testing taxonomy and introduces no runtime behavior or clear diff-only hazard; documentation lint could not be completed because Vale is unavailable.

Was this helpful? React 👍 or 👎

_{Open Bits AI session}

_{🤖 Datadog Autotest · Commit 11a3ac3 · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}