Unit tests for services

📘What it really is

• Services receive their repository (Module 43), so tests give them the in-memory one:

import { describe, it, expect, beforeEach } from "vitest";

describe("enquiryService.close", () => {
  let repo: InMemoryEnquiryRepo;
  beforeEach(() => { repo = new InMemoryEnquiryRepo([sampleNewEnquiry]); });

  it("closes a new enquiry with a note", async () => {
    const result = await close(repo, "E101", "Called back", staffUser);
    expect(result.status).toBe("closed");
    expect(result.closedBy).toBe(staffUser.id);
  });

  it("refuses to close an already closed enquiry", async () => {
    await close(repo, "E101", "First", staffUser);
    await expect(close(repo, "E101", "Second", staffUser)).rejects.toThrow(ConflictError);
  });
});

• beforeEach gives every test fresh data, so tests don't affect each other.
• Test schemas directly too: valid data passes, and each kind of bad data fails with the expected message.
• Dates and randomness make tests unpredictable. Pass in the current time or an id generator, or use Vitest's fake timers (vi.useFakeTimers()), so results are the same every run.