Exercise 2: Testing computeFullPath() — Possible Solution
====================================================================

THE FUNCTION UNDER TEST
------------------------------
// db/pages.ts
async function computeFullPath(slug: string, parentId: number | null): Promise<string> {
  if (!parentId) return slug;
  const [parent] = await db.select().from(pages).where(eq(pages.id, parentId));
  return `${parent.fullPath}/${slug}`;
}

TEST 1 — NO PARENT
------------------------------
computeFullPath('programming', null) resolves to 'programming' - the
early return fires immediately since parentId is null, with no
database query issued at all.

TEST 2 — WITH A REAL PARENT
------------------------------
Given a page already stored with id: 1 and fullPath: 'programming',
computeFullPath('java', 1) queries that row, finds
parent.fullPath === 'programming', and resolves to
'programming/java' - the parent's own full path plus the new slug,
joined with a single slash.

WHY THIS WORKS AS AN ANSWER
------------------------------
It correctly traces both branches of computeFullPath() - the
no-parent early return and the real-parent database lookup - and
correctly shows the resulting full_path value each one produces.