(v6.x backport) test: enable setuid/setgid test

test/parallel/test-process-setuid-setgid.js

@@ -0,0 +1,48 @@
+'use strict';
+
+const common = require('../common');
+
+const assert = require('assert');
+
+if (common.isWindows) {
+  // uid/gid functions are POSIX only
+  assert.strictEqual(process.getuid, undefined);
+  assert.strictEqual(process.setuid, undefined);
+  assert.strictEqual(process.getgid, undefined);
+  assert.strictEqual(process.setgid, undefined);
+  return;
+}
+
+assert.throws(() => {
+  process.setuid('fhqwhgadshgnsdhjsdbkhsdabkfabkveybvf');
+}, /^Error: setuid user id does not exist$/);
+
+// If we're not running as super user...
+if (process.getuid() !== 0) {
+  assert.doesNotThrow(() => {
+    process.getgid();
+    process.getuid();
+  });
+
+  assert.throws(
+    () => { process.setgid('nobody'); },
+    /^Error: (EPERM, .+|setgid group id does not exist)$/
+  );
+
+  assert.throws(
+    () => { process.setuid('nobody'); },
+    /^Error: EPERM, /
+  );
+  return;
+}
+
+// If we are running as super user...
+const oldgid = process.getgid();
+process.setgid('nobody');
+const newgid = process.getgid();
+assert.notStrictEqual(newgid, oldgid);
+
+const olduid = process.getuid();
+process.setuid('nobody');
+const newuid = process.getuid();
+assert.notStrictEqual(newuid, olduid);