What's the purpose of this unit test?

// src/quotes/tags.service.test.ts
describe('tags.service', () => {
  beforeEach(() => {
    vi.restoreAllMocks()
  })
  describe('upsertTags', () => {
    it('should return a list of tagIds', async () => {
      prismaMock.$transaction.mockResolvedValueOnce([1, 2, 3])
      const tagIds = await TagService.upsertTags(['tag1', 'tag2', 'tag3'])
      expect(tagIds).toStrictEqual([1, 2, 3])
    })
  })
})

// src/quotes/tags.service.ts
// ...
export const upsertTags = async (tags: string[]) => {
  return await prisma.$transaction(async tx => {
    // ...
  })
}