Add tests to support deprecated event listeners

lib/client.js

@@ -374,10 +374,8 @@ Client.prototype.query = function (config, values, callback) {
     }
   } else {
     query = new Query(config, values, callback)
-    result = query.callback ? undefined : new global.Promise((resolve, reject) => {
-      query.once('end', resolve)
-      query.once('error', reject)
-    })
+    query._deprecateListeners()
+    result = query
   }
 
   if (this.binary && !query.binary) {

lib/query.js

@@ -53,6 +53,25 @@ Query.prototype.requiresPreparation = function() {
   return this.values.length > 0;
 };
 
+Query.prototype.then = function(onSuccess, onFailure) {
+  return this._getPromise().then(onSuccess, onFailure);
+};
+
+Query.prototype.catch = function(callback) {
+  return this._getPromise().catch(callback);
+};
+
+Query.prototype._getPromise = function() {
+  if (this._promise) return this._promise;
+  this._promise = new Promise(function(resolve, reject) {
+    this.once('end', resolve);
+    this.once('error', reject);
+  }.bind(this));
+  return this._promise;
+};
+
+Query.prototype._deprecateListeners = function() {
+}
 
 //associates row metadata from the supplied
 //message with this query object

test/integration/client/deprecated-listener-tests.js

@@ -0,0 +1,30 @@
+const helper = require('./test-helper')
+const pg = helper.pg
+const suite = new helper.Suite()
+
+suite.test('Query with a callback should still support event-listeners', (done) => {
+  const client = new pg.Client()
+  const sink = new helper.Sink(3, 1000, () => {
+    client.end()
+    done()
+  })
+  client.connect()
+  const query = client.query('SELECT NOW()', (err, res) => {
+    sink.add()
+  })
+  query.on('row', () => sink.add())
+  query.on('end', () => sink.add())
+})
+
+suite.test('Query with a promise should still support event-listeners', (done) => {
+  const client = new pg.Client()
+  const sink = new helper.Sink(3, 1000, () => {
+    client.end()
+    done()
+  })
+  client.connect()
+  const query = client.query('SELECT NOW()')
+  query.on('row', () => sink.add())
+  query.on('end', () => sink.add())
+  query.then(() => sink.add())
+})