tests: ability to trace tests via RUST_LOG

in legacy_client tests only

Author: dare3path

Cargo.toml

@@ -41,6 +41,8 @@ http-body-util = "0.1.0"
 tokio = { version = "1", features = ["macros", "test-util", "signal"] }
 tokio-test = "0.4"
 pretty_env_logger = "0.5"
+tracing-subscriber = { version = "0.3", features = ["env-filter", "fmt"] }
+ctor = "0.2"
 
 [target.'cfg(any(target_os = "linux", target_os = "macos"))'.dev-dependencies]
 pnet_datalink = "0.35.0"

tests/legacy_client.rs

@@ -1068,10 +1068,25 @@ fn connection_poisoning() {
 // copy/paste-able without relying on external 'use' statements. Detailed inline
 // comments explain the purpose and logic of each section.
 
-//XXX: cargo test --features="http1,http2,server,client-legacy" --test legacy_client -- test_connection_error_propagation test_incomplete_message_error --nocapture
+//XXX: can manually run like this:
+// $ RUST_LOG=hyper=trace cargo test --features="http1,http2,server,client-legacy" --test legacy_client -- test_connection_error_propagation test_incomplete_message_error --nocapture
+// $ RUST_LOG=hyper=trace cargo test --all-features --test legacy_client -- --nocapture
+// $ cargo test --all-features --test legacy_client
+// --nocapture is actually not necessary to see the trace messages.
 
 use std::error::Error; // needed for .source() eg. error[E0599]: no method named `source` found for struct `hyper_util::client::legacy::Error` in the current scope
 
+#[cfg(test)]
+#[ctor::ctor]
+fn init_tracing() {
+    // Initialize a tracing subscriber that logs to stderr with TRACE level.
+    // Use EnvFilter to respect RUST_LOG directives (e.g., hyper=trace).
+    tracing_subscriber::fmt()
+        .with_env_filter(tracing_subscriber::EnvFilter::from_default_env())
+        .with_writer(std::io::stderr)
+        .init();
+}
+
 // Helper function to debug byte slices by attempting to interpret them as UTF-8.
 // If the bytes are valid UTF-8, they are printed as a string; otherwise, they are
 // printed as a raw byte array. This aids in debugging tokio_test::io::Mock mismatches.