docs(samples): add quickstart code for ExportAssets (#50)

asset/snippets/package.json

@@ -14,9 +14,19 @@
       "**/*.test.js"
     ]
   },
-  "scripts": {},
+  "scripts": {
+    "test": "mocha system-test --timeout 20000"
+  },
   "dependencies": {
-    "@google-cloud/asset": "^0.1.0"
+    "@google-cloud/asset": "^0.1.0",
+    "@google-cloud/storage": "^2.3.0",
+    "express": "^4.16.4",
+    "uuid": "^3.3.2",
+    "yargs": "^12.0.0"
   },
-  "devDependencies": {}
+  "devDependencies": {
+    "@google-cloud/nodejs-repo-tools": "^3.0.0",
+    "mocha": "^5.2.0",
+    "sinon": "^7.0.0"
+  }
 }

asset/snippets/system-test/quickstart.test.js

@@ -0,0 +1,51 @@
+/**
+ * Copyright 2018, 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
+ *
+ *    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.
+ */
+
+'use strict';
+
+const assert = require('assert');
+const path = require('path');
+const test = require('mocha');
+const tools = require('@google-cloud/nodejs-repo-tools');
+const util = require('util');
+const uuid = require('uuid');
+const cwd = path.join(__dirname, '..');
+const cmd = 'node quickstart.js';
+
+const {Storage} = require('@google-cloud/storage');
+
+const storage = new Storage();
+const bucketName = `asset-nodejs-${uuid.v4()}`;
+const bucket = storage.bucket(bucketName);
+
+test.describe('quickstart sample tests', () => {
+  test.before(tools.checkCredentials);
+  test.before(async () => {
+    await bucket.create();
+  });
+
+  test.after(async () => {
+    await bucket.delete();
+  });
+
+  test.it('should export assets to specified path', async () => {
+    const dumpFilePath = util.format('gs://%s/my-assets.txt', bucketName);
+    await tools.runAsyncWithIO(`${cmd} export-assets ${dumpFilePath}`, cwd);
+    const file = await bucket.file('my-assets.txt');
+    const [exists] = await file.exists();
+    assert.ok(exists);
+    await file.delete();
+  });
+});