MultiforaDB/tests/spec/README.md

MongoDB spec tests

PLAN D2 makes the official MongoDB JSON specification suites the gate for command semantics: it turns "maximally compatible" into a concrete list of test files rather than a judgement call. This directory holds the runner and the committed scorecard.

bash tests/spec/fetch.sh                  # pinned suites (~175 files, gitignored)
zig build                                 # the runner spawns this binary
node tests/spec/run.js                    # run everything
node tests/spec/run.js --scorecard        # ... and rewrite scorecard.txt
node tests/spec/run.js --file find.json --verbose
node tests/spec/run.js --url mongodb://127.0.0.1:27020   # use a server you started

What is pinned, and why both halves matter

• Suites: mongodb/specifications @ 615e0f9, in fetch.sh.
• Driver: mongodb@7.5.0, via tests/e2e/package-lock.json.

A scorecard is only comparable across milestones if both are pinned — otherwise a delta could be an upstream test change rather than an engine change. Bump either one in its own commit and re-record the scorecard in that same commit.

The suites are fetched rather than vendored: they are someone else's corpus, upstream rewrites them wholesale, and a pinned commit gives the same reproducibility without putting them in this repo's history.

Scope

source/crud/tests/unified/ — 175 files. The aggregate tests live there too (aggregate*.json), so this one directory is PLAN M0's "crud + aggregate".

The runner implements the unified test format's Evaluating Matches algorithm as written in the spec, including the two rules that decide whether a result is a real pass:

• extra keys in the actual document are tolerated only in a root document;
• numeric types (int32 / int64 / double) compare flexibly.

Supported: client/database/collection entities, initialData, outcome, expectError (code, codeName, contains, labels, errorResponse), expectEvents, saveResultAsEntity, runOnRequirements gating, and the $$type, $$exists, $$unsetOrMatches, $$matchesEntity, $$matchesHexBytes operators.

expectEvents compares the commands the driver actually sent against the expectation, exact in number and in order, with command and reply matched as root documents so the driver's own additions (lsid, $db) are allowed. It is what makes a pass mean the engine answered correctly and was asked the right question — 354 of the 487 cases declare events, and before this was asserted a case could send the wrong command and still be counted a pass. Scorecards recorded before it landed are not comparable; there, pass was an upper bound by construction.

Still unasserted within events, each reported as SKIP at the point of assertion: cmap and sdam event types, ignoreExtraEvents, hasServiceId, hasServerConnectionId, and maxTimeMS in an expected command — the runner puts CSOT timeoutMS on every client, and CSOT overwrites maxTimeMS with what is left of that budget, so the value on the wire is the harness's. That is the only assertion this runner declines to make; one case in the corpus is affected.

Not supported, each reported as SKIP with a reason and never as PASS: session and bucket entities (M4 / GridFS), failPoint, client-side encryption, testRunner operations, and any operation or matcher the runner does not know.

MFDB_DUMP_EVENTS=1 prints each case's observed command stream, which is the fastest way to tell a wrong answer from a command the driver never sent.

Reading the scorecard

scorecard.txt records the totals, a per-file breakdown, and every non-passing case with its reason. The distinction that matters:

• FAIL — the engine answered, and answered differently from the spec. Real work. An operation that never answered inside --op-timeout-ms (default 10 s, enforced by the driver itself via CSOT timeoutMS) is also a FAIL, because "no answer" is a result. There is a second, much longer --case-timeout-ms backstop for a hang the driver cannot see; if it ever fires, treat the run with suspicion — see the trap below.
• SKIP — nobody claims anything. Either the suite needs a feature whose milestone has not landed, or the runner does not implement it yet.

M0's gate (PLAN D7.6) is only that the harness exists and the baseline is recorded. A red baseline is the expected state, so run.js exits 0 as long as it ran; it is a measuring tool, not a pass/fail gate. Later milestones move the numbers, and each one commits the new scorecard (PLAN D9).

A trap worth knowing about: the harness can invent failures

The first baseline attempt reported ~77 timeout FAILs that did not exist. Every case from one point onward timed out, while a ping from a separate process answered instantly — which read convincingly as a server-side wedge, and was not.

The cause was in this runner. buildEntities opened MongoClients, and a case that timed out before it returned left them unclosed; each one keeps a connection pool and a heartbeat timer. Once enough accumulated, Node's event loop was starved badly enough that the per-case timer fired before operations could finish. Then every later case "failed".

Two things guard it now: per-test clients are owned by the caller and closed unconditionally, including on a partial failure; and the run ends by checking how many timers are still active, warning loudly if the answer is more than a handful.

The general rule, since it will come up again: a run with a long unbroken tail of timeouts is a harness bug until proven otherwise. Confirm it by running the first timing-out file on its own — if it passes in isolation, the failures are this runner's, not the engine's.

... but the third time it was the engine

A later attempt produced 166 timeout FAILs starting at file 70. I first blamed machine load — a concurrent zig build test against a then-3-second budget — and that was wrong. The evidence against it: the collapse reproduced on an idle machine, at the same file, with a 10 s budget.

The actual cause was a leaked catalog lock in the engine, and it is worth knowing how it hid. db-aggregate.json sends {aggregate: 1}, which names no collection; dispatch resolved the namespace after taking the catalog lock and bailed with a plain return, holding it shared forever. A leaked shared lock is invisible to readers, so the server stayed perfectly responsive — an external prober got ok 15ms right through the hang — and only the next write that had to take the catalog exclusive to create a collection blocked. The failure therefore surfaced one file later, on a different connection, as a client-side timeout with nothing pointing at its cause.

Two lessons for using this runner:

• A healthy-looking server does not exonerate the engine. Probe with the operation that is actually stuck, not with ping.

• The driver's own command log is the fastest way in. It showed an insert sitting for exactly socketTimeoutMS against an idle engine, which is what turned a week-long-looking mystery into a five-line fix:

  MONGODB_LOG_COMMAND=debug MONGODB_LOG_PATH=stderr \
    node tests/spec/run.js --skip 68 --limit 2 2>drv.log
  

--skip/--limit exist for exactly this: the collapse reduced to a reproducible two-file window, which is what made it tractable.

Still worth recording the baseline on an otherwise idle machine, and do not tighten --op-timeout-ms to make a run finish sooner — a tight budget turns load into apparent engine failures, which is how I misdiagnosed this once already.