core/sibling-exists — require a companion file

Insist that a file has a partner — its test, its types, its story file. Path-only: it decides from the filename, without reading any content.

What it catches

A file that’s supposed to come with a companion but doesn’t — e.g. a domain module with no .test.ts next to it.

Config

rules:
  - id: domain-has-test
    use: core/sibling-exists
    on: "src/domain/**/*.ts"          # files this applies to
    sibling: "{dir}/{name}.test.ts"   # the partner that must exist
    message: "Every domain module needs a sibling test."
Field What it does
on Glob(s) for the files the rule applies to.
sibling The required partner, as a template. Placeholders: {dir} (folder), {name} (filename without extension), {base} (filename with extension), {path} (full path without extension).
message The reason, shown on a block. 
src/domain/user.ts  +  src/domain/user.test.ts    ✓ passes
src/domain/order.ts (no order.test.ts)            ✗ blocked

Path-shape, not content. This only checks that the partner exists. To check what’s in it — e.g. that the test actually references the module’s exports — use core/symbols-in-sibling.