docs(changeStream): update changestream examples

Updates changeStream examples to use async/await

Fixes NODE-1533

test/examples/change_streams.js

@@ -0,0 +1,124 @@
+'use strict';
+
+const setupDatabase = require('../functional/shared').setupDatabase;
+const expect = require('chai').expect;
+const MongoClient = require('../../lib/mongo_client');
+
+describe('examples(change-stream):', function() {
+  let client;
+  let db;
+
+  before(async function() {
+    await setupDatabase(this.configuration);
+  });
+
+  beforeEach(async function() {
+    client = await MongoClient.connect(this.configuration.url());
+    db = client.db(this.configuration.db);
+
+    await db.collection('inventory').deleteMany({});
+  });
+
+  afterEach(async function() {
+    await client.close();
+    client = undefined;
+    db = undefined;
+  });
+
+  it('Open A Change Stream', {
+    metadata: { requires: { topology: ['replicaset'], mongodb: '>=3.6.0' } },
+    test: async function() {
+      setTimeout(async function() {
+        await db.collection('inventory').insertOne({ a: 1 });
+      });
+
+      // Start Changestream Example 1
+      const collection = db.collection('inventory');
+      const changeStream = collection.watch();
+      const next = await changeStream.next();
+      // End Changestream Example 1
+
+      await changeStream.close();
+
+      expect(next)
+        .to.have.property('operationType')
+        .that.equals('insert');
+    }
+  });
+
+  it('Lookup Full Document for Update Operations', {
+    metadata: { requires: { topology: ['replicaset'], mongodb: '>=3.6.0' } },
+    test: async function() {
+      await db.collection('inventory').insertOne({ a: 1, b: 2 });
+      setTimeout(async function() {
+        await db.collection('inventory').updateOne({ a: 1 }, { $set: { a: 2 } });
+      });
+
+      // Start Changestream Example 2
+      const collection = db.collection('inventory');
+      const changeStream = collection.watch({ fullDocument: 'updateLookup' });
+      const next = await changeStream.next();
+      // End Changestream Example 2
+
+      await changeStream.close();
+
+      expect(next)
+        .to.have.property('operationType')
+        .that.equals('update');
+      expect(next)
+        .to.have.property('fullDocument')
+        .that.has.all.keys(['_id', 'a', 'b']);
+    }
+  });
+
+  it('Resume a Change Stream', {
+    metadata: { requires: { topology: ['replicaset'], mongodb: '>=3.6.0' } },
+    test: async function() {
+      setTimeout(async function() {
+        await db.collection('inventory').insertOne({ a: 1 });
+        await db.collection('inventory').insertOne({ b: 2 });
+      });
+
+      // Start Changestream Example 3
+      const collection = db.collection('inventory');
+      const changeStream = collection.watch();
+      const change1 = await changeStream.next();
+
+      const resumeAfter = change1._id;
+      changeStream.close();
+
+      const newChangeStream = collection.watch({ resumeAfter });
+      const change2 = await newChangeStream.next();
+      // End Changestream Example 3
+
+      await newChangeStream.close();
+
+      expect(change1).to.have.nested.property('fullDocument.a', 1);
+      expect(change2).to.have.nested.property('fullDocument.b', 2);
+    }
+  });
+
+  it('Modify Change Stream Output', {
+    metadata: { requires: { topology: ['replicaset'], mongodb: '>=3.6.0' } },
+    test: async function() {
+      setTimeout(async function() {
+        await db.collection('inventory').insertOne({ username: 'alice' });
+      });
+
+      // Start Changestream Example 4
+      const pipeline = [
+        { $match: { 'fullDocument.username': 'alice' } },
+        { $addFields: { newField: 'this is an added field!' } }
+      ];
+      const collection = db.collection('inventory');
+      const changeStream = collection.watch(pipeline);
+      const next = await changeStream.next();
+      // End Changestream Example 4
+
+      await changeStream.close();
+
+      expect(next).to.have.nested.property('fullDocument.username', 'alice');
+      expect(next).to.have.property('newField', 'this is an added field!');
+    }
+  });
+});