test: retry pubsub test, as it relies on many moving parts (#186)

adds retry with exponential backoff to the flaky pubsub test.

fixes: #184, #185

container-analysis/snippets/test/containerAnalysis.test.js

@@ -17,6 +17,7 @@
 const {assert} = require('chai');
 const {describe, it, before, after, afterEach, beforeEach} = require('mocha');
 const cp = require('child_process');
+const {delay} = require('./util');
 const uuid = require('uuid');
 
 const {ContainerAnalysisClient} = require('@google-cloud/containeranalysis');
@@ -343,7 +344,10 @@ describe('pubsub', () => {
     await pubsub.subscription(subscriptionId).delete();
   });
 
-  it('should get count of occurrences from pubsub topic', async () => {
+  it('should get count of occurrences from pubsub topic', async function() {
+    this.retries(3);
+    await delay(this.test);
+
     const occurrenceCount = 3;
     const pubSubOccurrenceReq = {
       parent: formattedParent,

container-analysis/snippets/test/util.js

@@ -0,0 +1,28 @@
+// Copyright 2020 Google LLC
+//
+// 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
+//
+//     https://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.
+
+// ML tests frequently run into concurrency and quota issues, for which
+// retrying with a backoff is a good strategy:
+module.exports = {
+  async delay(test) {
+    const retries = test.currentRetry();
+    if (retries === 0) return; // no retry on the first failure.
+    // see: https://cloud.google.com/storage/docs/exponential-backoff:
+    const ms = Math.pow(2, retries) * 1000 + Math.random() * 2000;
+    return new Promise(done => {
+      console.info(`retrying "${test.title}" in ${ms}ms`);
+      setTimeout(done, ms);
+    });
+  },
+};