ADR 003: Adopt Jest as the backend test runner

• Status: accepted
• Date: 2025-11-14

Context

The backend initially used node:test for unit tests. As the codebase grew, we needed a more expressive test runner with mocks, spies, snapshots, and coverage reporting.

Decision

Adopt Jest as the primary test runner for the backend. Update npm scripts and migrate existing tests accordingly.

Consequences

• Richer testing features (mocks, spies, snapshots, coverage).
• Industry-standard tooling.
• Slightly heavier setup for ESM and transforms.