Don't use getters

src/index.js

@@ -10,34 +10,26 @@ const createCert = require('create-cert');
 const createTestServer = opts => createCert(opts && opts.certificate)
 	.then(cert => {
 		const app = express();
-		app.caCert = cert.caKeys.cert;
-		Object.defineProperty(app, 'url', {
-			get: () => typeof app.port === 'undefined' ? undefined : `http://localhost:${app.port}`
-		});
-		Object.defineProperty(app, 'sslUrl', {
-			get: () => typeof app.sslPort === 'undefined' ? undefined : `https://localhost:${app.sslPort}`
-		});
-
 		const server = http.createServer(app);
 		const sslServer = https.createServer(cert.keys, app);
 
+		app.caCert = cert.caKeys.cert;
+
 		app.listen = () => Promise.all([
-			getPort().then(port => {
-				app.port = port;
-				return pify(server.listen.bind(server))(port);
-			}),
-			getPort().then(sslPort => {
-				app.sslPort = sslPort;
-				return pify(sslServer.listen.bind(sslServer))(sslPort);
-			})
+			getPort().then(port => pify(server.listen.bind(server))(port).then(() => {
+				app.url = `http://localhost:${port}`;
+			})),
+			getPort().then(sslPort => pify(sslServer.listen.bind(sslServer))(sslPort).then(() => {
+				app.sslUrl = `https://localhost:${sslPort}`;
+			}))
 		]);
 
 		app.close = () => Promise.all([
 			pify(server.close.bind(server))().then(() => {
-				app.port = undefined;
+				app.url = undefined;
 			}),
 			pify(sslServer.close.bind(sslServer))().then(() => {
-				app.sslPort = undefined;
+				app.sslUrl = undefined;
 			})
 		]);