Mocking ES modules in Jest — cannot mock import statements

jest.mock() does not work with ES module imports. The original module is still imported despite the mock.

jest.mock() must be at the top of the file — Jest hoists it automatically. For ESM: (1) Use jest.unstable_mockModule(). (2) Use dynamic import() after jest.mock(). (3) Prefer dependency injection over mocking. (4) Use __mocks__ directory. (5) For named exports: jest.mock('./module', () => ({ myFunc: jest.fn() })). With Vitest: vi.mock() handles ESM natively.

ES module imports are hoisted and resolved before code runs. jest.mock() is hoisted by Babel/Jest transform, but native ESM modules are loaded by Node's module system which runs before transforms.