1c72aa8938
27 cases, recorded before a line of the evaluator is written, which is the
whole point of having built the recorder first: the expectations come from
mongod 8.3.7 rather than from what the implementation is about to do.
The corpus reads 1 pass / 26 fail, and the one pass is the unknown-operator
refusal M2 already answers correctly. Expressions are exercised through
`$group` because `_id` and the accumulator arguments are the only expression
positions that exist until `$addFields` and `$project`'s computed fields land;
testing them anywhere else would be testing a stage that is not there.
Ten things the recording settled that guessing would have got wrong:
$add over a missing field or null null -- not an error, and not 0
$add over a string error 7157723
$divide by zero error 4848401
$mod of -5 by 4 -1, the dividend's sign
$lt of a number and a string true, canonical type order
$and over -5 truthy
$not of a missing field true
$switch, no branch and no default error 40069
two operators in one expression error 15983, *not* $group's 40238
$subtract with one operand error 16020
The six error codes are in `ErrorCode` already, so the evaluator's refusals and
its runtime failures have somewhere measured to land. The evaluator itself is
the next commit and is not started.
191/191 unit tests, crud corpus unchanged at 201/90/196.
94 lines
3.8 KiB
Markdown
94 lines
3.8 KiB
Markdown
# The aggregation corpus
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`mongodb/specifications` has no aggregation suite. The thirteen
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`aggregate-*.json` files this project runs come from `crud` and test the
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aggregate *command* — cursors, read concern, the write stages, collation,
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`let`. They touch stages barely and expressions not at all: `$lookup`,
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`$unwind`, `$facet`, `$addFields` and `$replaceRoot` appear nowhere in the
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pinned corpus. That is PLAN amendment A6, and this directory is its
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consequence: M2.5 has to bring its own gate.
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## The one rule
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**Inputs are authored here; expectations are measured against a real mongod.**
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A corpus we write is a corpus that can encode our own bugs as expectations, and
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it would then agree with us forever. So `sources/*.json` holds documents and
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pipelines and nothing else, and `record.js` asks mongod 8.3.7 what each pipeline
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answers. It is the same discipline that corrected three assumptions in M1's
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session work and every error code in M2 — the alternative, in both cases, would
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have shipped.
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## Running it
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```sh
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node tests/spec/run.js --suite-dir tests/spec/aggregate
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```
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The same runner as the crud corpus, pointed elsewhere. Sharing it is the point:
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the entity model, the matchers, the skip accounting and `expectEvents` come for
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free, and a second runner would drift from the first exactly where it mattered.
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`--scorecard` is refused with `--suite-dir`: `tests/spec/scorecard.txt` is the
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crud corpus's record and the milestones are compared against it.
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## Re-recording
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```sh
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mongod --port 27099 --dbpath /tmp/mongo-corpus &
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node tests/spec/aggregate/record.js --mongod-port 27099
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```
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Writes `<name>.json` for every `sources/<name>.json`. The generated files are
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committed: they *are* the corpus, and regenerating them is how a disagreement
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with mongod gets re-measured rather than argued about.
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Two things to know when adding cases:
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- **End a `$group` pipeline with a `$sort`.** Group output order is unspecified,
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and a case that depended on it would fail for the wrong reason on either
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server.
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- **Errors record the code, not the message.** Message text is mongod's to
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change between releases; a corpus that pinned it would break for the wrong
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reason.
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Leave out any case whose answer depends on a server newer than the 4.4 this
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server reports — recording it from mongod 8.x and judging it against a 4.4
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answer measures the version gap, not the engine.
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## Where it stands
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Recorded against mongod 8.3.7. At the M2 tip it read 9 pass / 10 fail; with the
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accumulators in:
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```
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group-accumulators.json 18 pass 1 fail 0 skip
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expressions.json 1 pass 26 fail 0 skip
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```
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`group-accumulators` found its first real disagreement on the way to 18:
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`$avg` over a group with no numeric value is `null`, not `0`, and a divisor
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that counted documents rather than numbers would have passed every test
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anybody would think to write by hand.
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`expressions.json` is the next tier's spec, recorded and not yet implemented --
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its one pass is the unknown-operator refusal M2 already answers correctly.
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Expressions are exercised through `$group`, because `_id` and the accumulator
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arguments are the only expression positions that exist until `$addFields` and
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`$project`'s computed fields land.
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What recording it settled, none of which is guessable:
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| `$add` over a missing field or null | `null`, not an error and not `0` |
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| `$add` over a string | error 7157723 |
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| `$divide` by zero | error 4848401 |
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| `$mod` of -5 by 4 | `-1` — the dividend's sign |
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| `$lt` of a number and a string | `true` — canonical type order |
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| `$and` over `-5` | truthy |
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| `$not` of a missing field | `true` |
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| `$switch` with no branch and no default | error 40069 |
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| two operators in one expression document | error 15983, *not* `$group`'s 40238 |
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| `$subtract` with one operand | error 16020 |
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