1 files changed, 37 insertions, 0 deletions
diff --git a/third_party/rust/tracing/tests/max_level_hint.rs b/third_party/rust/tracing/tests/max_level_hint.rs
new file mode 100644
index 0000000000..63d3af6357
--- /dev/null
+++ b/third_party/rust/tracing/tests/max_level_hint.rs
@@ -0,0 +1,37 @@
+use tracing::Level;
+use tracing_mock::*;
+
+#[cfg_attr(target_arch = "wasm32", wasm_bindgen_test::wasm_bindgen_test)]
+#[test]
+fn max_level_hints() {
+    // This test asserts that when a subscriber provides us with the global
+    // maximum level that it will enable (by implementing the
+    // `Subscriber::max_level_hint` method), we will never call
+    // `Subscriber::enabled` for events above that maximum level.
+    //
+    // In this case, we test that by making the `enabled` method assert that no
+    // `Metadata` for spans or events at the `TRACE` or `DEBUG` levels.
+    let (subscriber, handle) = subscriber::mock()
+        .with_max_level_hint(Level::INFO)
+        .with_filter(|meta| {
+            assert!(
+                dbg!(meta).level() <= &Level::INFO,
+                "a TRACE or DEBUG event was dynamically filtered: "
+            );
+            true
+        })
+        .event(event::mock().at_level(Level::INFO))
+        .event(event::mock().at_level(Level::WARN))
+        .event(event::mock().at_level(Level::ERROR))
+        .done()
+        .run_with_handle();
+
+    tracing::subscriber::set_global_default(subscriber).unwrap();
+
+    tracing::info!("doing a thing that you might care about");
+    tracing::debug!("charging turboencabulator with interocitor");
+    tracing::warn!("extremely serious warning, pay attention");
+    tracing::trace!("interocitor charge level is 10%");
+    tracing::error!("everything is on fire");
+    handle.assert_finished();
+}