jest/prefer-to-have-length

Require toHaveLength() instead of comparing the length property

fixable

When expect(users.length).toBe(2) fails, the message shows two numbers. expect(users).toHaveLength(2) also prints the value it measured, so you see which items are missing or extra.

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:

bunfig.toml
[lint.rules]
"jest/prefer-to-have-length" = "error" # or "warn"

Examples#

example.ts2 problems
import { expect, test } from "@jest/globals";

test("finds the active users", () => {
  const users = findUsers({ active: true });
  expect(users.length).toBe(2);
  expect(users[0].roles.length).not.toEqual(0);
});
example.tsNo problems
import { expect, test } from "@jest/globals";

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);
});