test(samples): Refactor AWS S3 Test Credentials Source (#133)

Also allows the S3 client to be configured in a separate step.

Author: d-goog

storagetransfer/test/aws-request.test.js

@@ -31,10 +31,7 @@ describe('aws-request', () => {
   let gcsSinkBucket;
 
   before(async () => {
-    assert(
-      process.env.AWS_ACCESS_KEY_ID && process.env.AWS_SECRET_ACCESS_KEY,
-      'environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY are required'
-    );
+    testBucketManager.setupS3();
 
     projectId = await testBucketManager.getProjectId();
     awsSourceBucket = await testBucketManager.generateS3Bucket();

storagetransfer/test/utils/bucket.js

@@ -27,7 +27,6 @@ const uuid = require('uuid');
 class BucketManager {
   constructor() {
     this.client = new StorageTransferServiceClient();
-    this.s3 = new AWS.S3({apiVersion: '2006-03-01'});
     this.storage = new Storage();
 
     /**
@@ -45,6 +44,10 @@ class BucketManager {
     this.s3Buckets = [];
   }
 
+  setupS3(options = {}) {
+    this.s3 = new AWS.S3({apiVersion: '2006-03-01', ...options});
+  }
+
   async getProjectId() {
     if (!this._cachedProjectId) {
       this._cachedProjectId = await this.storage.getProjectId();