Setup Tests

Use this skill to bootstrap or repair the test harness for a TypeScript + Effect repository.

When To Use

• •The repo has no test runner configured.
• •bun run test or bun run test:coverage does not exist.
• •@effect/vitest is missing for Effect-first tests.
• •Coverage settings are missing or below required policy.

Only run this setup when the user asks for test-harness installation or repair.

Prerequisites

• •Package manager is Bun.
• •TypeScript project already exists (tsconfig.json present).
• •User approved dependency and config changes.

Setup Steps

1. •Install required dev dependencies.

bun add -d vitest @effect/vitest @vitest/coverage-v8

1. •Ensure test scripts exist in package.json.

{
  "scripts": {
    "test": "vitest run",
    "test:watch": "vitest",
    "test:coverage": "vitest run --coverage"
  }
}

1. •Add vitest.config.ts with explicit include/exclude and coverage policy.

import { defineConfig } from "vitest/config";

export default defineConfig({
  test: {
    include: ["src/**/*.test.ts"],
    exclude: ["src/env.ts"],
    coverage: {
      provider: "v8",
      reporter: ["text", "html"],
      thresholds: {
        lines: 100,
        functions: 100,
        branches: 100,
        statements: 100,
      },
    },
  },
});

1. •Validate scaffold-level conventions.

• •Co-locate tests as src/**/*.test.ts.
• •Use @effect/vitest for Effect-centric tests.
• •Use vi from vitest for mocks and env stubs.
• •Keep quality-gate scripts available: test, test:watch, test:coverage.

1. •Add a baseline test only if no tests exist yet.

import { describe, expect, it } from "@effect/vitest";
import { Effect } from "effect";

describe("smoke", () => {
  it.effect("runs Effect test harness", () =>
    Effect.gen(function* () {
      expect(1 + 1).toBe(2);
    }),
  );
});

1. •Run the full verification commands.

bun run typecheck
bun run lint
bun run test
bun run test:coverage

1. •If the template was intentionally stripped of test scaffolding, reintroduce:

• •vitest, @effect/vitest, @vitest/coverage-v8 dev dependencies
• •test, test:watch, test:coverage scripts
• •vitest.config.ts
• •at least one src/**/*.test.ts file

Troubleshooting

• •Missing coverage provider:
  • •Verify @vitest/coverage-v8 is installed.
• •ESM/CJS import errors:
  • •Confirm package.json type and tsconfig module settings are compatible with Vitest.
• •Coverage below threshold:
  • •Add tests for missing branches before lowering thresholds.
• •Effect tests not recognized:
  • •Confirm imports come from @effect/vitest, not plain vitest, for Effect test files.

Hand-Off To Other Skills

• •After setup succeeds, use write-tests for feature and bug-test implementation.
• •If tracing/log correlation is also requested, use setup-otel.

References

• •https://vitest.dev/guide/
• •https://vitest.dev/config/
• •https://vitest.dev/guide/coverage
• •https://effect-ts.github.io/effect/docs/vitest
• •https://www.npmjs.com/package/@effect/vitest