test-in-tests-folder

Flags a unit test in a separate tests directory instead of beside its subject.

Deterministic checkAdvises by default

Why this rule

Test Files

A unit test sits beside its source file: src/auth/AuthService.ts → src/auth/AuthService.unit.test.ts.
Scenario suites: when one boundary genuinely needs more than one test file (a pipeline with distinct monorepo/nested/park scenarios), qualify the name — <File>.<scenario>.unit.test.ts, e.g. runImplementPipeline.monorepo.unit.test.ts. The first segment must name a real source file in the folder; the qualifier is camelCase. A test file whose subjects span several source files is a split candidate, not a naming exception — one subject per test file.
A test imports its subject from the subject's own file: a test beside its source imports the file it tests (./AuthService), never an index file (./index) — an import through one loads every file it re-exports to reach one name. A test inside a module may import that module's other files too; a test outside it imports only the module's public files, as any other caller would.
Shared test helpers, mocks, and fixtures live outside src/ in the package's test-support directories (tests/helpers/, test/mocks/, test/fixtures/, a __mocks__/ folder beside the module it doubles); only test files themselves sit beside their source. Test-support code under src/ would read as production source — to scanners and humans alike.
First import: import { expect, describe, test, jest } from '@jest/globals'; — but include jest only when the file actually uses jest.fn/jest.mock/jest.spyOn, and import beforeEach/afterEach/afterAll only when genuinely needed (with setup factories and config-level mock cleanup, most files need none). An unused import fails noUnusedLocals/lint.
The first describe matches the name of the class or function under test. Keep describe blocks flat — scenario variants come from setup() parameters, not nested describe + beforeEach pyramids. When you do nest, prefix with when ... (condition) or for ... (variant).

Test files live adjacent to the file they test — never in separate __tests__/ directories.

Examples

The check flags the incorrect code and passes the correct code. Each example is a small repo, because this rule looks across files. It opens on the file that matters; the other files are the repo around it.

Incorrect

srcfeaturetests

src/feature/getLabel.ts

export const getLabel = ({ name }: { name: string }): string => name.trim();

Correct

srcfeature

src/feature/getLabel.ts

export const getLabel = ({ name }: { name: string }): string => name.trim();

Configure

Block"blocking"Stops a run when a file the run changed breaks the rule.
Advise"advisory"Reports it and hands it to the refactor agent. Never stops a run.
Default
Off"off"Not checked. Use it when your own linter already enforces the rule.

Add this to your lightsout.config.json, then change the value.

lightsout.config.json

{
	"standards-checks": {
		"test-in-tests-folder": "advisory"
	}
}