mock: `MockCollector` can't differentiate between contextual and explicit roots

[hds]

Bug Report

Version

master branch, tracing-mock isn't released yet.

Probably also happens on v0.1.x branch, I haven't checked, but that code is the same.

Crates

tracing-mock

Description

Expecting an explicit root or a contextual root will accept either indescriminately. The following test should panic, but it doesn't.

#[test]
fn explicit_vs_contextual_root() {
    use tracing_mock::{collector, expect};

    let (collector, handle) = collector::mock()
        .new_span(expect::span().with_contextual_parent(None))
        .new_span(expect::span().with_explicit_parent(None))
        .new_span(expect::span().with_contextual_parent(None))
        .new_span(expect::span().with_explicit_parent(None))
        .run_with_handle();

    tracing::collect::with_default(collector, || {
        tracing::info_span!("contextual_root");
        tracing::info_span!(parent: None, "explicit_root");
        tracing::info_span!(parent: None, "explicit_root");
        tracing::info_span!("contextual_root");
    });

    handle.assert_finished();
}