Move to newest Jest version & TypeScript

[rene-leanix]

This is a test-branch to check if testdouble-jest can be run with TypeScript (and the newest version of Jest).

[searls]

I don't understand -- did you intend for this to be a PR against the main repo?

[rene-leanix]

No, sorry, this was merely intended as a show case for #7. That's why I created this as a draft PR, but would have been better to create the PR just for my fork. Will close it now.

[RA80533]

Use import { default as td } (or, since you have esModuleInterop enabled, import td) instead of import * as td, @rene-leanix. td will be an entirely different shape for the wildcard import—imagine it as a collection of all the exports from the module, including a default export (which is what you actually want).

Just out of curiosity, does Jest not work for your use case? It has built-in mocking, etc.

[rene-leanix]

To answer your question, @RA80533, we ended up using Jest's own mocking and jest-when (with a small addition of our own to create mock return values). Here's some example code:

jest.enableAutomock();
jest.unmock('@app/spec/mocks'); // file with`when()` and other test-helpers
jest.unmock('@app/helpers'); // file to be tested

//... imports

afterAll(() => {
  jest.disableAutomock();
  cleanupWhenMocks();
});

describe('getTimeSpan()', () => {
  it('returns correct timespan based on expected function calls', () => {
    const zoomLevel = mock<TimeUnit>();
    const today = when(startOfYear).calledWith(expect.any(Date)).mockReturnValueOnce();
    const minus10Years = when(addUnits).calledWith(today, 'year', -10).mockReturnValueOnce();
    const plus10Years = when(addUnits).calledWith(today, 'year', 10).mockReturnValueOnce();
    const begin = when(getBeginOfUnit).calledWith(minus10Years, zoomLevel).mockReturnValueOnce();
    const end = when(startOfNextUnit).calledWith(plus10Years, zoomLevel).mockReturnValueOnce();

    const timespan = getTimeSpan(zoomLevel);

    expect(timespan).toStrictEqual({ unit: zoomLevel, begin, end });
  });
});

All variables in this example are mocked with a simple mock()-function that returns an otherwise object with a unique identifier. That simplifies the test a lot and makes look like the actual code a lot when it comes to function calls.