test(bind): add test to wait for data to be ready in collections

Previous test was succeeding because of mock being synchronous on updates but in real world
scenarios, those are delayed. So I forced delay (1 tick with setTimeout(0)) to make the test always
fail. (it was occasionnaly failing before)

test/refs-collections.spec.js

@@ -26,18 +26,41 @@ beforeEach(async () => {
   await tick()
 })
 
+// This makes sure some tests fail by delaying callbacks
+function delayUpdate (ref, time = 0) {
+  const onSnapshot = ref.onSnapshot.bind(ref)
+  ref.onSnapshot = fn => onSnapshot(async (...args) => {
+    await delay(time)
+    console.log('I waited for', time)
+    fn(...args)
+  })
+}
+
 test('binds refs on collections', async () => {
   await vm.$bind('items', collection)
 
-  // XXX dirty hack until $bind resolves when all refs are bound
-  await delay(5)
-
   expect(vm.items).toEqual([
     { ref: { isA: true }},
     { ref: { isB: true }}
   ])
 })
 
+test('waits for array to be fully populated', async () => {
+  const c = db.collection().doc()
+  await c.update({ isC: true })
+  await collection.add({ ref: c })
+  // force callback delay
+  delayUpdate(c)
+  const data = await vm.$bind('items', collection)
+
+  expect(data).toEqual(vm.items)
+  expect(vm.items).toEqual([
+    { ref: { isA: true }},
+    { ref: { isB: true }},
+    { ref: { isC: true }}
+  ])
+})
+
 test('binds refs when adding to collection', async () => {
   await vm.$bind('items', collection)
   const c = db.collection().doc()