Trace stdout from test-proxy (#2274)

* Trace stdout from test-proxy

This is a big refactor of the test-proxy wrapper that will precede other work. This will help diagnose issues that, in the past,  you could only do if you started the test-proxy separately and remembered to pass `PROXY_MANUAL_START=true` when testing.

* Trace stderr as ERROR level

* Resolve PR feedback

sdk/core/azure_core_test/README.md

@@ -105,6 +105,26 @@ cargo test
 If you get errors, they could indicate regressions in your tests or perhaps variables or random data wasn't saved correctly.
 Review any data you generate or use not coming from the service.
 
+## Troubleshooting
+
+Like all Azure SDK client libraries, the `azure_core_test` crate writes information with the target rooted in the crate name
+followed by any modules in which the span was created e.g., `azure_core_test::proxy`.
+Because this crate is used to test Azure SDK client libraries and developers will most likely want to see fewer traces from this crate,
+the log levels used are a level lower than typical client libraries:
+
+- `INFO` includes only important information e.g., the version of `test-proxy` and on what port it's listening.
+- `DEBUG` includes when a test recording or playback has started and stopped.
+- `TRACE` includes details like communications with the `test-proxy` itself.
+
+The `azure_core_test` crate also traces useful information that the `test-proxy` process itself writes to `stdout` using the `test-proxy` target and the `TRACE` logging level.
+
+You can configure tracing using the [`RUST_LOG`](https://docs.rs/env_logger) environment variable.
+For example, if you wanted to see debug information from all sources by default but see `test-proxy` messages written to `stdout` you'd run:
+
+```bash
+RUST_LOG=debug,test-proxy=trace cargo test
+```
+
 [PowerShell]: https://learn.microsoft.com/powershell/scripting/install/installing-powershell
 [Test Proxy]: https://github.com/Azure/azure-sdk-tools/blob/main/tools/test-proxy/Azure.Sdk.Tools.TestProxy/README.md
 [Test Resources]: https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/TestResources/README.md

sdk/core/azure_core_test/examples/test_proxy.rs

@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
-use clap::Parser;
+use clap::{ArgAction, Parser};
 
 #[cfg(not(target_arch = "wasm32"))]
 #[tokio::main]
@@ -46,33 +46,48 @@ async fn main() -> Result<(), Box<dyn std::error::Error>> {
 #[derive(Debug, Parser)]
 #[command(about = "Starts the Test-Proxy service", version)]
 struct Args {
+    /// Bind to any available port.
+    ///
+    /// If not set, only port `5000` will be tried.
+    /// You can start the `test-proxy` service this way
+    /// and pass `PROXY_MANUAL_START=true` when running `cargo test` to easily view trace information.
+    #[arg(long)]
+    auto: bool,
+
     /// Allow insecure upstream SSL certs.
     #[arg(long)]
     insecure: bool,
 
     /// Number of seconds to automatically shut down when no activity.
     #[arg(long, default_value_t = 300)]
-    pub auto_shutdown_in_seconds: u32,
+    auto_shutdown_in_seconds: u32,
 
     /// Enable verbose logging.
-    #[arg(short, long)]
-    verbose: bool,
+    ///
+    /// Trace level `INFO` is used by default.
+    /// Pass `-v` to enable `DEBUG` level tracing,
+    /// or `-vv` to enable `TRACE` level tracing.
+    #[arg(short, long, action = ArgAction::Count)]
+    verbose: u8,
 }
 
 impl Args {
     #[cfg(not(target_arch = "wasm32"))]
     fn trace_level(&self) -> tracing::level_filters::LevelFilter {
-        if self.verbose {
-            return tracing::level_filters::LevelFilter::DEBUG;
+        use tracing::level_filters::LevelFilter;
+        match self.verbose {
+            0 => LevelFilter::INFO,
+            1 => LevelFilter::DEBUG,
+            _ => LevelFilter::TRACE,
         }
-        tracing::level_filters::LevelFilter::INFO
     }
 }
 
 #[cfg(not(target_arch = "wasm32"))]
 impl From<Args> for azure_core_test::proxy::ProxyOptions {
     fn from(args: Args) -> Self {
         Self {
+            auto: args.auto,
             insecure: args.insecure,
             auto_shutdown_in_seconds: args.auto_shutdown_in_seconds,
         }