test: getgroups() may contain duplicate GIDs

Some systems may have multiple group names with the same group ID, in
which case getgroups() returns duplicate values, where `id -G` will
filter the duplicates. Unique and sort the arrays so they can be
compared.

Backport-PR-URL: nodejs/node#12468
PR-URL: nodejs/node#10389
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gibson Fahnestock <gibfahn@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

test/parallel/test-process-getgroups.js

@@ -1,21 +1,23 @@
 'use strict';
 const common = require('../common');
-const assert = require('assert');
-const exec = require('child_process').exec;
+
+// Check `id -G` and `process.getgroups()` return same groups.
 
 if (common.isOSX) {
   common.skip('Output of `id -G` is unreliable on Darwin.');
   return;
 }
+const assert = require('assert');
+const exec = require('child_process').exec;
 
 if (typeof process.getgroups === 'function') {
-  const groups = process.getgroups();
+  const groups = unique(process.getgroups());
   assert(Array.isArray(groups));
   assert(groups.length > 0);
   exec('id -G', function(err, stdout) {
-    if (err) throw err;
-    const real_groups = stdout.match(/\d+/g).map(Number);
-    assert.strictEqual(groups.length, real_groups.length);
+    assert.ifError(err);
+    const real_groups = unique(stdout.match(/\d+/g).map(Number));
+    assert.deepStrictEqual(groups, real_groups);
     check(groups, real_groups);
     check(real_groups, groups);
   });
@@ -24,3 +26,7 @@ if (typeof process.getgroups === 'function') {
 function check(a, b) {
   for (let i = 0; i < a.length; ++i) assert.notStrictEqual(b.indexOf(a[i]), -1);
 }
+
+function unique(groups) {
+  return [...new Set(groups)].sort();
+}