add test for interleaved scopes in trees

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

tracing-subscriber/tests/layer_filters/trees.rs

@@ -53,3 +53,96 @@ fn basic_trees() {
     info_handle.assert_finished();
     with_target_handle.assert_finished();
 }
+
+#[test]
+fn filter_span_scopes() {
+    fn target_layer(target: &'static str) -> (ExpectLayer, subscriber::MockHandle) {
+        layer::named(format!("target_{}", target))
+            .enter(span::mock().with_target(target).at_level(Level::INFO))
+            .event(
+                event::msg("hello world")
+                    .in_scope(vec![span::mock().with_target(target).at_level(Level::INFO)]),
+            )
+            .exit(span::mock().with_target(target).at_level(Level::INFO))
+            .done()
+            .run_with_handle()
+    }
+
+    let (a_layer, a_handle) = target_layer("a");
+    let (b_layer, b_handle) = target_layer("b");
+    let (info_layer, info_handle) = layer::named("info")
+        .enter(span::mock().with_target("b").at_level(Level::INFO))
+        .enter(span::mock().with_target("a").at_level(Level::INFO))
+        .event(event::msg("hello world").in_scope(vec![
+            span::mock().with_target("a").at_level(Level::INFO),
+            span::mock().with_target("b").at_level(Level::INFO),
+        ]))
+        .exit(span::mock().with_target("a").at_level(Level::INFO))
+        .exit(span::mock().with_target("b").at_level(Level::INFO))
+        .done()
+        .run_with_handle();
+
+    let full_scope = vec![
+        span::mock().with_target("b").at_level(Level::TRACE),
+        span::mock().with_target("a").at_level(Level::INFO),
+        span::mock().with_target("b").at_level(Level::INFO),
+        span::mock().with_target("a").at_level(Level::TRACE),
+    ];
+    let (all_layer, all_handle) = layer::named("all")
+        .enter(span::mock().with_target("a").at_level(Level::TRACE))
+        .enter(span::mock().with_target("b").at_level(Level::INFO))
+        .enter(span::mock().with_target("a").at_level(Level::INFO))
+        .enter(span::mock().with_target("b").at_level(Level::TRACE))
+        .event(event::msg("hello world").in_scope(full_scope.clone()))
+        .event(
+            event::msg("hello to my target")
+                .with_target("a")
+                .in_scope(full_scope.clone()),
+        )
+        .event(
+            event::msg("hello to my target")
+                .with_target("b")
+                .in_scope(full_scope),
+        )
+        .exit(span::mock().with_target("b").at_level(Level::TRACE))
+        .exit(span::mock().with_target("a").at_level(Level::INFO))
+        .exit(span::mock().with_target("b").at_level(Level::INFO))
+        .exit(span::mock().with_target("a").at_level(Level::TRACE))
+        .done()
+        .run_with_handle();
+
+    let a_layer = a_layer.with_filter(filter::filter_fn(|meta, _| {
+        let target = meta.target();
+        target == "a" || target == module_path!()
+    }));
+
+    let b_layer = b_layer.with_filter(filter::filter_fn(|meta, _| {
+        let target = meta.target();
+        target == "b" || target == module_path!()
+    }));
+
+    let info_stack = info_layer
+        .and_then(a_layer)
+        .and_then(b_layer)
+        .with_filter(LevelFilter::INFO);
+
+    let _subscriber = tracing_subscriber::registry()
+        .with(info_stack)
+        .with(all_layer)
+        .set_default();
+
+    {
+        let _a1 = tracing::trace_span!(target: "a", "a/trace").entered();
+        let _b1 = tracing::info_span!(target: "b", "b/info").entered();
+        let _a2 = tracing::info_span!(target: "a", "a/info").entered();
+        let _b2 = tracing::trace_span!(target: "b", "b/trace").entered();
+        tracing::info!("hello world");
+        tracing::debug!(target: "a", "hello to my target");
+        tracing::debug!(target: "b", "hello to my target");
+    }
+
+    all_handle.assert_finished();
+    info_handle.assert_finished();
+    a_handle.assert_finished();
+    b_handle.assert_finished();
+}