Testing Framework Selection

Context

We need a testing framework that supports both Backend (NestJS/Node.js) and Future Frontend (React/Web) within a monorepo structure. The tool must handle ESM (ES Modules) natively and provide high performance.

Comparison (2026 Landscape)

Feature	Vitest	Jest	Bun Test
ESM Support	Native (Excellent)	Complex/Requires Workarounds	Native
Performance	Ultra-fast (Vite-based)	Slower (Process overhead)	Fastest
Ecosystem	Compatible with Jest API	Industry Standard	Limited
DX	Instant Watch Mode	Slower re-runs	Instant

Decision

Vitest.

Rationale

1. ESM Native: Unlike Jest, Vitest doesn't struggle with type: module and Top-level await, which are core to our project.
2. Monorepo Efficiency: By installing it at the root, we maintain a single version for all packages while allowing specific configurations (e.g., SWC for NestJS decorators).
3. Speed: Leveraging esbuild/swc ensures that tests don't become a bottleneck as the project grows.
4. Compatibility: It supports the same describe/it/expect syntax as Jest, making it easy for contributors.

Consequences

• Specific plugins (like unplugin-swc) are required to handle NestJS decorators.