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TEST-001: New Services Require Unit Tests

AttributeValue
CategoryTesting Standards
Default Severityerror
Applicable FilesService files (*.service.ts)

Why It Exists (Rationale)​

In a layered architecture, services house the core domain calculations, transaction handling, state machines, and business rules of an application. Service-layer tests represent the highest Return on Investment (ROI) among automated tests:

  • They run purely in-memory and execute in milliseconds.
  • They do not require spinning up HTTP servers, browsers, or network proxies.
  • They directly validate business correctness under boundary and edge-case conditions.

Introducing a new service file without an accompanying unit test file directly increases technical debt and introduces untested failure modes into production.

Bad Example​

PR File Changes:
├── src/services/billing.service.ts   (Created)
└── src/controllers/billing.controller.ts (Created)
// ❌ No billing.service.test.ts or tests/billing.service.ts included in PR

Good Example​

PR File Changes:
├── src/services/billing.service.ts        (Created)
├── src/services/billing.service.test.ts   (Created)
└── src/controllers/billing.controller.ts  (Created)
// src/services/billing.service.test.ts
import { describe, it, expect } from "vitest";
import { BillingService } from "./billing.service.js";

describe("BillingService", () => {
  it("computes prorated charge accurately across leap months", () => {
    const service = new BillingService();
    const result = service.calculateProration(100, 15, 30);
    expect(result).toBe(50);
  });
});

How It's Detected​

For every file classified as a service in the pull request, ArchStandards evaluates the file manifest of the PR to ensure a corresponding test file exists matching standard test naming patterns (<name>.test.ts, <name>.spec.ts, tests/<name>.ts, __tests__/<name>.ts).

Exception Configuration​

exceptions:
  - rule: "TEST-001"
    path: "src/services/experimental-stub.service.ts"
    reason: "Prototype service under active research spike; tests deferred to follow-up PR."