Rulvar API reference / @rulvar/testing / readCassette
Function: readCassette()
function readCassette(path): VcrCassette;Defined in: packages/testing/src/vcr.ts:698
Parses a cassette file (one header line plus one JSON row per line). The header must declare cassette format v: 1: the format version gates parsing itself, while hashVersion (whose support window is checked by replay) only gates request identity and never substitutes for it, so a future incompatible format refuses loudly instead of being read as v1. Every documented header field (kind, v, an integer hashVersion, a date string recordedAt) and row field (adapterId, model, requestHash, request, caps, events, an optional string provider, an optional nonempty usageSemantics, an optional nonnegative integer occurrence) is checked here, and the nested structures are validated in depth (v1.30.0 review P3): the request must be a plain object, every event must be a member of the canonical ChatEvent vocabulary with its required payload and Usage numeric invariants, and caps must carry every ModelCaps field (with the optional pricing table checked when present). Unknown extra FIELDS are tolerated for forward compatibility. Event stream SEMANTICS (one trailing terminal per row) and adapter consistency across rows (provider, usageSemantics, caps agreement) are deliberately not checked at read time; replay enforces them before serving anything (v1.29.0 review P3), so reading never blocks inspecting a well formed file. Parse and shape failures throw a typed ConfigError naming the cassette path and line (v1.28.0 review P3).
Parameters
| Parameter | Type |
|---|---|
path | string |