tools,test: throw if common.PORT used in parallel tests

common.PORT should not be used in parallelized tests. (There can be a
port collision if another tests requests an arbitrary open port from the
operating system and ends up getting common.PORT before a test that uses
common.PORT uses the port.) In such a situation, throw an error.

PR-URL: nodejs#17559
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>

test/common/index.js

@@ -40,7 +40,16 @@ const noop = () => {};
 // gets tools to ignore it by default or by simple rules, especially eslint.
 let tmpDirName = '.tmp';
 
-exports.PORT = +process.env.NODE_COMMON_PORT || 12346;
+Object.defineProperty(exports, 'PORT', {
+  get: () => {
+    if (+process.env.TEST_PARALLEL) {
+      throw new Error('common.PORT cannot be used in a parallelized test');
+    }
+    return +process.env.NODE_COMMON_PORT || 12346;
+  },
+  enumerable: true
+});
+
 
 exports.isWindows = process.platform === 'win32';
 exports.isWOW64 = exports.isWindows &&

tools/test.py

@@ -532,7 +532,8 @@ def Run(self):
 
     try:
       result = self.RunCommand(self.GetCommand(), {
-        "TEST_THREAD_ID": "%d" % self.thread_id
+        "TEST_THREAD_ID": "%d" % self.thread_id,
+        "TEST_PARALLEL" : "%d" % self.parallel
       })
     finally:
       # Tests can leave the tty in non-blocking mode. If the test runner