xdist master cant see workers' workeroutput when using --forked

まず、issue に記載されている pytest_sessionfinish フックと pytest_testnodedown フックを、pytest-forked による --forked の処理および参照されている newhooks.py と併せて追跡します。記載されている Python、pytest、pytest-xdist、pytest-forked のバージョンで再現します。--forked が有効な場合に、pytest_testnodedown 中に worker の統計情報を master が利用できれば完了です。

Hi fellas.

I am building a tests profiler for collecting various statistics before/during test cases execution.
Since we use pytest-xdist, I decided its finally time to look into how new xdist hooks from newhooks.py work and try to get as much value out of them as possible, since doing shenanigans with locks and writing output to tmp files is pretty ugly.

I have finished my profiler MVP, and it was working nicely, until I tried to run it in our jenkins which uses --forked option.
setup
python-3.8.10
pytest-7.4.3
pytest-xdist-3.3.1
pytest-forked-1.6.0

ISSUE
Turned out no stats are being displayed when I use this option.
Inside pytest_testnodedown hook, where master node is collecting and aggregating collected statistics from all worker nodes, the node.workeroutput attribute is simply empty.

Is there some workaround for this, on how to properly send data from workers to master when using --forked? Am I just missing something?

Here are 2 most important hooks used for collecting and aggregating all the statistics.

    @pytest.hookimpl(hookwrapper=True, tryfirst=True)
    def pytest_sessionfinish(self):
        worker_id = get_xdist_worker_id(self)
        if worker_id != "master":
            # NOTE: Execnet can't serialize custom classes. Serialization has to be
            # implemented for everything we want to send in-between master and workers
            self.config.workeroutput[
                f"{worker_id}-stats"
            ] = self._profiling_stats.serialize()
        yield

    @pytest.hookimpl(trylast=True)
    def pytest_testnodedown(self, node):
        worker_id = node.workerinput["workerid"]
        node_stats = node.workeroutput[f"{worker_id}-stats"]
        node_stats = ProfilerNamespaceUnit.deserialize(node_stats)
        self._profiling_stats.merge_trees(node_stats)