bun:test/prefer-to-contain

Require toContain() instead of comparing the result of includes() with a boolean

has suggestions

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:

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

Examples#

example.ts2 problems
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);
});
example.tsNo problems
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:

example.tsNo problems
import { expect, test } from "bun:test";

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