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ADR 0022: Hybrid Cross-Language Testing for Service Subsystems

Status: Proposed Date: 2026-05-24

Context

Spikard's test harness is HTTP-centric: fixtures carry http.handler / http.request / http.expected_response, and the alef-generated e2e mock-server (e2e/rust/src/main.rs) only understands HTTP shapes. The toolbox subsystems are not HTTP — they publish and consume messages, read and write keys and objects, enqueue jobs, and query databases. We must keep cross-language behavioral parity (ADR 0001) while also validating real-backend correctness, without dragging containerized brokers and databases into the polyglot CI matrix.

Decision

A three-layer hybrid strategy:

  • In-memory mock backend per subsystem, with no system dependencies, shipped in the bindings' default feature set: OpenDAL memory for storage, an in-process MemoryBroker for messaging, moka for cache, an in-memory queue for tasks, and SQLite :memory: for the database. These drive cross-language end-to-end parity.
  • Fixture schema, version 2: add storage, messaging, cache, db, and tasks operation blocks alongside http (for example, messaging: publish { topic, payload } → expected_handled[] with the asserted ack). The alef e2e generator and the e2e/rust mock-server are extended to drive these against the memory backend through each binding's public API. WebAssembly auto-skips them, as it already skips HTTP-shaped fixtures. This is the one alef change the toolbox commits to.
  • Containerized Rust integration tests per subsystem crate, behind a dev-feature, exercising real Kafka, NATS, RabbitMQ, Redis, MQTT, PostgreSQL, and MinIO for ack/redelivery, offset commit, TTL eviction, pool exhaustion, and cron firing. These run in Rust CI only, not the polyglot matrix.

Consequences

  • Subsystem correctness (real-broker semantics) is validated once in Rust per ADR 0001; binding parity is validated across all languages via the memory-backend fixtures. Bindings are not asked to run containers.
  • The fixture schema and the e2e generator gain a non-HTTP vocabulary — a generator change scoped here and sequenced in roadmap phase 0 so later subsystems can add fixtures immediately.
  • Memory backends must match real-backend observable semantics closely enough that a passing fixture means a passing real backend for the covered behavior; divergence is caught by the Rust integration layer.

References

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