Repository: nodejs/node
Pull request: test: verify tracing channel doesn't swallow unhandledRejection

Add a test to verify that `TracingChannel.tracePromise` doesn't swallow `unhandledRejection` events in case no then/catch handler is set by user.

Refs: https://github.com/nodejs/node/pull/59944#discussion_r2366118170

<!--
Before submitting a pull request, please read:

- the CONTRIBUTING guide at https://github.com/nodejs/node/blob/HEAD/CONTRIBUTING.md
- the commit message formatting guidelines at
  https://github.com/nodejs/node/blob/HEAD/doc/contributing/pull-requests.md#commit-message-guidelines

For code changes:
1. Include tests for any bug fixes or new features.
2. Update documentation if relevant.
3. Ensure that `make -j4 test` (UNIX), or `vcbuild test` (Windows) passes.

If you believe this PR should be highlighted in the Node.js CHANGELOG
please add the `notable-change` label.

Developer's Certificate of Origin 1.1

By making a contribution to this project, I certify that:

(a) The contribution was created in whole or in part by me and I
    have the right to submit it under the open source license
    indicated in the file; or

(b) The contribution is based upon previous work that, to the best
    of my knowledge, is covered under an appropriate open source
    license and I have the right under that license to submit that
    work with modifications, whether created in whole or in part
    by me, under the same open source license (unless I am
    permitted to submit under a different license), as indicated
    in the file; or

(c) The contribution was provided directly to me by some other
    person who certified (a), (b) or (c) and I have not modified
    it.

(d) I understand and agree that this project and the contribution
    are public and that a record of the contribution (including all
    personal information I submit with it, including my sign-off) is
    maintained indefinitely and may be redistributed consistent with
    this project or the open source license(s) involved.
-->


Changed files:
filename: test/parallel/test-diagnostics-channel-tracing-channel-promise-unhandled.js
patch: @@ -0,0 +1,38 @@
+'use strict';
+
+const common = require('../common');
+const dc = require('diagnostics_channel');
+const assert = require('assert');
+
+const channel = dc.tracingChannel('test');
+
+const expectedError = new Error('test');
+const input = { foo: 'bar' };
+const thisArg = { baz: 'buz' };
+
+process.on('unhandledRejection', common.mustCall((reason) => {
+  assert.deepStrictEqual(reason, expectedError);
+}));
+
+function check(found) {
+  assert.deepStrictEqual(found, input);
+}
+
+const handlers = {
+  start: common.mustCall(check),
+  end: common.mustCall(check),
+  asyncStart: common.mustCall(check),
+  asyncEnd: common.mustCall(check),
+  error: common.mustCall((found) => {
+    check(found);
+    assert.deepStrictEqual(found.error, expectedError);
+  })
+};
+
+channel.subscribe(handlers);
+
+// Set no then/catch handler to verify unhandledRejection happens
+channel.tracePromise(function(value) {
+  assert.deepStrictEqual(this, thisArg);
+  return Promise.reject(value);
+}, input, thisArg, expectedError);