Exercise 2: Testing getBreadcrumb() — Possible Solution
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THE FUNCTION UNDER TEST
------------------------------
Per this chapter:

async function getBreadcrumb(pageId) {
  const crumbs = [];
  let currentId = pageId;
  while (currentId) {
    const current = await prisma.page.findUnique({ where: { id: currentId } });
    if (!current) break;
    crumbs.unshift(current);
    currentId = current.parentId;
  }
  return crumbs;
}

TEST SETUP
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Using a real three-level-deep chain, e.g. "Programming" (top-level, id
1, parentId null) -> "Web Development" (id 2, parentId 1) -> "React
Fundamentals" (id 3, parentId 2), calling getBreadcrumb(3) should
produce the full ancestor chain for the deepest page.

TRACING THE WALK
------------------------------
currentId starts at 3. First iteration fetches page 3 ("React
Fundamentals"), unshifts it (crumbs = [React Fundamentals]), then
currentId becomes 2 (its own parentId). Second iteration fetches page 2
("Web Development"), unshifts it to the FRONT (crumbs = [Web
Development, React Fundamentals]), then currentId becomes 1. Third
iteration fetches page 1 ("Programming"), unshifts it (crumbs =
[Programming, Web Development, React Fundamentals]), then currentId
becomes null (Programming's own parentId), ending the loop.

CONFIRMATION
------------------------------
The final crumbs array reads root-to-leaf, in the correct display
order: Programming, Web Development, React Fundamentals - exactly the
order a breadcrumb nav bar should display them in, left to right.

WHY THIS WORKS AS AN ANSWER
------------------------------
It correctly traces why unshift() (adding to the front, not push()
which would add to the back) is what produces root-to-leaf order despite
the walk itself proceeding leaf-to-root, and confirms the result against
a real three-level page chain rather than a trivial one-level example
that wouldn't actually exercise the loop.