try to fix get port race condition unit test fail (no idea why yet)

src/helper-functions/impure/get-port.spec.ts

@@ -20,16 +20,14 @@
 // tslint:disable:no-shadowed-variable
 import test  from 'blue-tape'
 
-// import http      from 'http'
-// import express   from 'express'
 import net from 'net'
 
 import { getPort } from './get-port'
 
 test('getPort() for an available socket port', async t => {
-  const PORT = 8788
+  // const PORT = 8788
 
-  let port = await getPort(PORT)
+  let port = await getPort()
   let ttl = 17
 
   const serverList = []
@@ -42,7 +40,7 @@ test('getPort() for an available socket port', async t => {
       server.listen(port, '127.0.0.1')
       serverList.push(server)
 
-      port = await getPort(PORT)
+      port = await getPort()
 
     } catch (e) {
       t.fail('should not exception: ' + e.message + ', ' + e.stack)

src/helper-functions/impure/get-port.ts

 import net     from 'net'
 
+const DEFAULT_PORT = 38788
+
 /**
  *
  * @param port is just a suggestion.
@@ -11,8 +13,8 @@ import net     from 'net'
  * const DEFAULT_IANA_RANGE = {min: 49152, max: 65535}
  *
  */
-export function getPort (port: number): Promise<number> {
-  let tryPort = nextPort(port || 38788)
+export function getPort (port = DEFAULT_PORT): Promise<number> {
+  let tryPort = nextPort(port)
 
   return new Promise(resolve => {
     // https://gist.github.com/mikeal/1840641
@@ -39,13 +41,13 @@ export function getPort (port: number): Promise<number> {
   function nextPort (currentPort: number): number {
     const RANGE = 1733
     // do not use Math.random() here, because AVA will fork, then here will get the same random number, cause a race condition for socket listen
-    // const n = Math.floor(Math.random() * BETWEEN_RANGE)
+    const n = Math.floor(Math.random() * RANGE)
 
     /**
      * nano seconds from node: http://stackoverflow.com/a/18197438/1123955
      */
-    const [, nanoSeed] = process.hrtime()
-    const n = 1 + nanoSeed % RANGE // +1 to prevent same port
+    // const [, nanoSeed] = process.hrtime()
+    // const n = 1 + nanoSeed % RANGE // +1 to prevent same port
 
     if (currentPort + n > 65000) {
       return currentPort + n - RANGE