Challenge 1: Testing multiply(a, b) — Possible Solution
====================================================================

describe("multiply", () => {
  it("multiplies two positive numbers", () => {
    expect(multiply(3, 4)).toBe(12);
  });

  it("returns zero when multiplying by zero", () => {
    expect(multiply(5, 0)).toBe(0);
  });
});

WHY THIS WORKS AS AN ANSWER
------------------------------
The describe block groups both cases under the function's name,
matching this chapter's own anatomy example exactly. Two separate it
blocks cover two genuinely different behaviors worth testing
independently: the "normal" positive-number case, and the zero-edge
case specifically called out in the challenge — multiplying by zero
is a classic edge case worth its own explicit test, since a bug in
handling zero wouldn't necessarily show up in a general positive-number
test.

toBe is the correct matcher choice here (rather than toEqual) because
multiply returns a plain number — a primitive — and this chapter's own
warn-box specifically noted that toBe is meant for primitives, where
reference and value equality are the same thing.