jest/no-export

When another file imports from a test file, the whole test file runs, including its test() calls, so its tests run a second time as part of the importing file. Put shared helpers in a separate file.

The rule only checks files named like tests. That means the name ends in test or spec before the extension, such as cart.test.ts, or the file is under a __tests__ directory. A file with no test or it call can export anything.

Configure

Off by default. To turn it on:

[lint.rules]
"jest/no-export" = "error" # or "warn"

Examples

Reported:

import { expect, test } from "@jest/globals";

export function makeCart() {
  return { items: [] };
}

test("starts empty", () => {
  expect(makeCart().items).toEqual([]);
});

Not reported, with the helper in a separate file:

export function makeCart() {
  return { items: [] };
}

import { expect, test } from "@jest/globals";
import { makeCart } from "./helpers";

test("starts empty", () => {
  expect(makeCart().items).toEqual([]);
});

Exported types are reported too:

import { expect, test } from "@jest/globals";
import { makeCart } from "./helpers";

export type Cart = ReturnType<typeof makeCart>;

test("starts empty", () => {
  expect(makeCart().items).toEqual([]);
});