[W3C] Refactor W3C integration tests

Improve developer experience when troubleshooting failing tests (like I was in #6307) by logging both stderr and stdout and ignoring warnings in the upstream Python tests.

Author: martincostello

test/OpenTelemetry.Instrumentation.W3cTraceContext.Tests/W3CTraceContextTests.cs

@@ -37,8 +37,8 @@ public void W3CTraceContextTestSuiteAsync(string value)
     {
         // configure SDK
         using var tracerProvider = Sdk.CreateTracerProviderBuilder()
-        .AddAspNetCoreInstrumentation()
-        .Build();
+            .AddAspNetCoreInstrumentation()
+            .Build();
 
         var builder = WebApplication.CreateBuilder();
         using var app = builder.Build();
@@ -68,12 +68,14 @@ public void W3CTraceContextTestSuiteAsync(string value)
 
         app.RunAsync("http://localhost:5000/");
 
-        string result = RunCommand("python", "trace-context/test/test.py http://localhost:5000/");
+        (var stdout, var stderr) = RunCommand("python", "-W ignore trace-context/test/test.py http://localhost:5000/");
 
         // Assert
-        string lastLine = ParseLastLine(result);
+        // TODO: after W3C Trace Context test suite passes, it might go in standard output
+        string lastLine = ParseLastLine(stderr);
 
-        this.output.WriteLine("result:" + result);
+        this.output.WriteLine("[stderr]" + stderr);
+        this.output.WriteLine("[stdout]" + stdout);
 
         // Assert on the last line
         Assert.StartsWith("OK", lastLine, StringComparison.Ordinal);
@@ -84,7 +86,7 @@ public void Dispose()
         this.httpClient.Dispose();
     }
 
-    private static string RunCommand(string command, string args)
+    private static (string StdOut, string StdErr) RunCommand(string command, string args)
     {
         using var proc = new Process
         {
@@ -101,10 +103,12 @@ private static string RunCommand(string command, string args)
         };
         proc.Start();
 
-        // TODO: after W3C Trace Context test suite passes, it might go in standard output
-        var results = proc.StandardError.ReadToEnd();
+        var stdout = proc.StandardOutput.ReadToEnd();
+        var stderr = proc.StandardError.ReadToEnd();
+
         proc.WaitForExit();
-        return results;
+
+        return (stdout, stderr);
     }
 
     private static string ParseLastLine(string output)