bun:test/prefer-to-have-length

When expect(users.length).toBe(2) fails, the message shows two bare numbers. expect(users).toHaveLength(2) labels them as the expected and the received length. If the value has no length property, it says so instead of comparing undefined with 2.

The rule reports .length inside expect() when the matcher is toBe(), toEqual(), or toStrictEqual().

--fix rewrites the assertion.

Configure

Off by default. To turn it on:

[lint.rules]
"bun:test/prefer-to-have-length" = "error" # or "warn"

Examples

Reported:

import { expect, test } from "bun:test";

test("finds the active users", () => {
  const users = findUsers({ active: true });
  expect(users.length).toBe(2);
  expect(users[0].roles.length).not.toEqual(0);
});

Not reported:

import { expect, test } from "bun:test";

test("finds the active users", () => {
  const users = findUsers({ active: true });
  expect(users).toHaveLength(2);
  expect(users[0].roles).not.toHaveLength(0);
  expect(users.length).toBeGreaterThan(1);
});