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test: make live DNS tests robust instead of gated (closes #93)
The resolver's live-DNS tests failed nondeterministically, a different
subset each run. Three structural causes, all test-side:

- Burst fan-out. Every test in the package is parallel and the build
  hosts have many cores, so all ~35 iterative resolutions started at
  the same instant and, because queryServers walks rootServerList() in
  fixed order, hit the same root server within milliseconds. Root
  servers rate-limit that.
- No retry anywhere. One dropped UDP packet in a delegation chain
  failed a test outright.
- Unanimity assertions. TestQueryAllNameservers_AllReturnOK and
  _NXDomainFromAllNS required every one of a domain's nameservers to
  answer, with no tolerance for one being slow.

New internal/resolver/livedns_test.go addresses each: a package-wide
gate bounds how many live resolutions are in flight at once, every
live operation gets three attempts with exponential backoff and its
own deadline, and multi-nameserver assertions now need a strict
majority rather than unanimity. The retry predicate is deliberately
transport-level -- "did a nameserver answer at all" -- never the
assertion under test, so a resolver that answers incorrectly still
fails on the first attempt. A nameserver that stays silent is
tolerated; one that answers wrongly is not.

livedns_harness_test.go tests that machinery directly: quorum
arithmetic, status counting, the gate's concurrency bound, per-attempt
deadlines, and recovery from a transient failure. It touches no DNS.

Nothing is mocked, faked, stubbed, recorded, skipped or build-tagged,
and production resolver behaviour is unchanged.

Test caps move to the new org-wide values ruled at prompts issue 41:
60s hard cap, 20s target, 90s -timeout backstop. REPO_POLICIES.md is
re-vendored byte-identical from sneak/prompts rather than hand-edited,
which also picks up the golangci-lint paragraph this copy had drifted
behind on. TESTING.md's stale 30-second target follows to 60.

#93
2026-08-10 13:09:17 +00:00

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# Testing Policy
## DNS Resolution Tests
All resolver tests **MUST** use live queries against real DNS servers.
No mocking of the DNS client layer is permitted.
### Rationale
The resolver performs iterative resolution from root nameservers through
the full delegation chain. Mocked responses cannot faithfully represent
the variety of real-world DNS behavior (truncation, referrals, glue
records, DNSSEC, varied response times, EDNS, etc.). Testing against
real servers ensures the resolver works correctly in production.
### Constraints
- Tests hit real DNS infrastructure and require network access
- Test duration depends on network conditions; timeout tuning keeps
the suite within the 60-second target
- Query timeout is calibrated to 3× maximum antipodal RTT (~300ms)
plus processing margin
- Root server fan-out is limited to reduce parallel query load
- Flaky failures from transient network issues are acceptable and
should be investigated as potential resolver bugs, not papered over
with mocks or skip flags
### What NOT to do
- **Do not mock `DNSClient`** for resolver tests (the mock constructor
exists for unit-testing other packages that consume the resolver)
- **Do not add `-short` flags** to skip slow tests
- **Do not increase `-timeout`** to hide hanging queries
- **Do not modify linter configuration** to suppress findings