Cutting to the chase

In Vitest, this would work:

import {test, expect, vi} from "vitest"; import round from "lodash.round";

vi.mock("lodash.round", () => { return { default: (value) => 33 } })

test("roundup", () => { const no = 5.7; expect(round(no)).toBe(33); });

however if the mock is extracted to another file (say, to be reused across several tests), test will fail if it's imported after actual package it mocks:

import {test, expect, vi} from "vitest"; import round from "lodash.round"; import _ from "./roundmock";

test("roundup", () => { const no = 5.7; expect(round(no)).toBe(33); });

because the mock is imported after the actual package. This, however, will pass (note that the only difference is the order of imports):

import {test, expect, vi} from "vitest"; import _ from "./roundmock"; import round from "lodash.round";

test("roundup", () => { const no = 5.7; expect(round(no)).toBe(33); });

I guess that's because Vitest is hoisting mocks withing the file to happen before the imports, but if they're in separate files - the import will happen in actual import order.