vitest/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 rewrites the matcher. A test that passed with a value that isn't a boolean fails afterwards.

Configure#

Off by default. To turn it on:

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

Examples#

import { expect, test } from "vitest";

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

import { expect, test } from "vitest";

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

not.toBeTruthy() is reported too, and the rewrite is not.toBe(true), which passes for everything except true. Write toBe(false) instead.

import { expect, test } from "vitest";

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.

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