test: deflake test-common-expect-warning

The subprocess might exit before the data is flushed. Run the assertion after the `'end'` event is emitted. PR-URL: #42046 Reviewed-By: James M Snell <jasnell@gmail.com> Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com> Reviewed-By: Darshan Sen <raisinten@gmail.com>

Author: lpinca

test/parallel/test-common-expect-warning.js

@@ -36,9 +36,11 @@ if (process.argv[2] !== 'child') {
  child.stderr.on('data', (data) => {
  stderr += data;
  });
+ child.stderr.on('end', common.mustCall(() => {
+ assert.match(stderr, /Unexpected extra warning received/);
+ }));
  child.on('exit', common.mustCall((status) => {
  assert.notStrictEqual(status, 0);
- assert.match(stderr, /Unexpected extra warning received/);
  }));
  }
 } else {