jest/prefer-to-contain

When expect(tags.includes("new")).toBe(true) fails, the message only says that false is not true. expect(tags).toContain("new") prints the array and the item it looked for.

The rule reports expect(x.includes(y)) matched against true or false with toBe(), toEqual(), or toStrictEqual().

--fix rewrites the assertion, and adds or drops .not so it still tests the same thing.

Configure

Off by default. To turn it on:

[lint.rules]
"jest/prefer-to-contain" = "error" # or "warn"

Examples

Reported:

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

test("a draft is tagged", () => {
  const tags = getTags(draft);
  expect(tags.includes("draft")).toBe(true);
  expect(tags.includes("published")).toEqual(false);
});

Not reported:

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

test("a draft is tagged", () => {
  const tags = getTags(draft);
  expect(tags).toContain("draft");
  expect(tags).not.toContain("published");
});

toContain() has no equivalent for a start index, so this is allowed:

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

test("the tag is not first", () => {
  expect(getTags(draft).includes("draft", 1)).toBe(true);
});