bun:test/prefer-strict-boolean-matchers

toBeTruthy() passes for 1, "no" and {}. toBeFalsy() passes for 0, "", null and undefined. If a function should return a boolean and starts returning undefined, a test with toBeFalsy() still passes. toBe(false) fails.

--fix-suggestions rewrites the matcher. --fix doesn't, because a test that passed with a non-boolean value fails afterwards.

Configure#

Off by default. To turn it on:

[lint.rules]
"bun:test/prefer-strict-boolean-matchers" = "error" # or "warn"

Examples#

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

test("checks the password", () => {
  expect(isValid("correct horse")).toBeTruthy();
  expect(isValid("")).toBeFalsy();
});

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

test("checks the password", () => {
  expect(isValid("correct horse")).toBe(true);
  expect(isValid("")).toBe(false);
});

not.toBeTruthy() is reported too. The rewrite is toBe(false), not not.toBe(true), which would pass for everything except true.

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

test("rejects an empty password", () => {
  expect(isValid("")).not.toBeTruthy();
});

When not to use it#

Some tests only care that there's a value, like a match from String.prototype.match() or a non-empty string. In those tests, toBeTruthy() says what you mean.

bun:test/prefer-to-be-truthy and bun:test/prefer-to-be-falsy ask for the opposite. Don't turn them on together with this rule.