test: add coverage for app.listen() variants (#6476)

* test: add coverage for app.listen() variants - verify alternate signatures (port+host+backlog) - verify server.address() shape * fix linter issue --------- Co-authored-by: kuldeep <kuldeep@wanclouds.net>

Author: kgarg1

test/app.listen.js

@@ -24,4 +24,32 @@ describe('app.listen()', function(){
  })
  })
  })
+ it('accepts port + hostname + backlog + callback', function (done) {
+ const app = express();
+ const server = app.listen(0, '127.0.0.1', 5, function () {
+ const { address, port } = server.address();
+ assert.strictEqual(address, '127.0.0.1');
+ assert(Number.isInteger(port) && port > 0);
+ // backlog isn’t directly inspectable, but if no error was thrown
+ // we know it was accepted.
+ server.close(done);
+ });
+ });
+ it('accepts just a callback (no args)', function (done) {
+ const app = express();
+ // same as app.listen(0, done)
+ const server = app.listen();
+ server.close(done);
+ });
+ it('server.address() gives a { address, port, family } object', function (done) {
+ const app = express();
+ const server = app.listen(0, () => {
+ const addr = server.address();
+ assert(addr && typeof addr === 'object');
+ assert.strictEqual(typeof addr.address, 'string');
+ assert(Number.isInteger(addr.port) && addr.port > 0);
+ assert(typeof addr.family === 'string');
+ server.close(done);
+ });
+ });
 })