Add priming logic to integration tests to avoid backend cold start issues.

packages/firestore/test/integration/prime_backend.test.ts

@@ -0,0 +1,51 @@
+/**
+ * Copyright 2018 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as firestore from '@firebase/firestore-types';
+import { expect } from 'chai';
+import { EventsAccumulator } from './util/events_accumulator';
+import { withTestDoc } from './util/helpers';
+
+// Firestore databases can be subject to a ~30s "cold start" delay if they have not been used
+// recently, so before any tests run we "prime" the backend.
+
+const PRIMING_TIMEOUT_MS = 45000;
+
+before(
+  'Prime backend by waiting for a write to show up in the watch stream',
+  function(): Promise<void> {
+    this.timeout(PRIMING_TIMEOUT_MS);
+
+    return withTestDoc(/*persistence=*/ false, async doc => {
+      const accumulator = new EventsAccumulator<firestore.DocumentSnapshot>();
+      const unsubscribe = doc.onSnapshot(accumulator.storeEvent);
+
+      // Wait for watch to initialize and deliver first event.
+      await accumulator.awaitRemoteEvent();
+
+      // Use a transaction to perform a write without triggering any local events.
+      await doc.firestore.runTransaction(async txn => {
+        txn.set(doc, { value: 'done' });
+      });
+
+      // Wait to see the write on the watch stream.
+      const docSnap = await accumulator.awaitRemoteEvent();
+      expect(docSnap.get('value')).to.equal('done');
+
+      unsubscribe();
+    });
+  }
+);