core/packages/runtime-core/__tests__/componentSlots.spec.ts

import { ref, render, h, nodeOps, nextTick } from '@vue/runtime-test'

describe('component: slots', () => {
  // TODO more tests for slots normalization etc.

  test('should respect $stable flag', async () => {
    const flag1 = ref(1)
    const flag2 = ref(2)
    const spy = jest.fn()

    const Child = () => {
      spy()
      return 'child'
    }

    const App = {
      setup() {
        return () => [
          flag1.value,
          h(
            Child,
            { n: flag2.value },
            {
              foo: () => 'foo',
              $stable: true
            }
          )
        ]
      }
    }

    render(h(App), nodeOps.createElement('div'))
    expect(spy).toHaveBeenCalledTimes(1)

    // parent re-render, props didn't change, slots are stable
    // -> child should not update
    flag1.value++
    await nextTick()
    expect(spy).toHaveBeenCalledTimes(1)

    // parent re-render, props changed
    // -> child should update
    flag2.value++
    await nextTick()
    expect(spy).toHaveBeenCalledTimes(2)
  })
})