bun:test/prefer-to-contain

When expect(tags.includes("new")).toBe(true) fails, the message only says that false isn't 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-suggestions rewrites the assertion. --fix doesn't, because not every object with an includes() method works with toContain().

Configure

Off by default. To turn it on:

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

Examples

Reported:

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

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 "bun:test";

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

A start index has no equivalent in toContain(), so this is allowed:

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

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