[tests] Fix MarshalMethods startup logcat race in device test (#12195)

MarshalMethodsGCHangTests previously launched the app via RunProjectAndAssert and only then began logcat monitoring, which made the startup marker check racey under CI log volume. This change starts adb logcat monitoring first, then launches MainActivity via a callback once monitoring is attached, and clears logcat immediately before startup monitoring to keep the buffer focused on startup lines.

Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Author: jonathanpeppers

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/Utilities/DeviceTest.cs

@@ -355,7 +355,7 @@ protected TimeSpan ProfileFor (Func<bool> func, TimeSpan? timeout = null)
 			return stopwatch.Elapsed;
 		}
 
-		protected static bool MonitorAdbLogcat (Func<string, bool> action, string logcatFilePath, int timeout = 15)
+		protected static bool MonitorAdbLogcat (Func<string, bool> action, string logcatFilePath, int timeout = 15, Action? onMonitoringStarted = null)
 		{
 			string ext = Environment.OSVersion.Platform != PlatformID.Unix ? ".exe" : "";
 			string adb = Path.Combine (AndroidSdkPath, "platform-tools", "adb" + ext);
@@ -388,15 +388,21 @@ protected static bool MonitorAdbLogcat (Func<string, bool> action, string logcat
 						}
 					};
 					proc.BeginOutputReadLine ();
-					TimeSpan time = TimeSpan.FromSeconds (timeout);
-					while (!stdout_done.IsSet && !didActionSucceed && time.TotalMilliseconds > 0) {
-						proc.WaitForExit (10);
-						time -= TimeSpan.FromMilliseconds (10);
+					try {
+						onMonitoringStarted?.Invoke ();
+						TimeSpan time = TimeSpan.FromSeconds (timeout);
+						while (!stdout_done.IsSet && !didActionSucceed && time.TotalMilliseconds > 0) {
+							proc.WaitForExit (10);
+							time -= TimeSpan.FromMilliseconds (10);
+						}
+					} finally {
+						if (!proc.HasExited) {
+							proc.Kill ();
+						}
+						proc.WaitForExit ();
+						stdout_done.Wait ();
+						sw.Flush ();
 					}
-					proc.Kill ();
-					proc.WaitForExit ();
-					stdout_done.Wait ();
-					sw.Flush ();
 					return didActionSucceed;
 				}
 			}

tests/MSBuildDeviceIntegration/Tests/MarshalMethodsGCHangTests.cs

@@ -114,13 +114,15 @@ public void MarshalMethodsAppRuns ([Values (AndroidRuntime.CoreCLR, AndroidRunti
 
 		using var apkBuilder = CreateApkBuilder ();
 		Assert.True (apkBuilder.Install (proj), "Project should have installed.");
-		RunProjectAndAssert (proj, apkBuilder);
+		ClearAdbLogcat ();
 
 		const string expectedLogcatOutput = "XXX:OnStart done";
 		Assert.IsTrue (
 			MonitorAdbLogcat (
 				InstallAndRunTests.CreateLineChecker (expectedLogcatOutput),
-				logcatFilePath: Path.Combine (Root, apkBuilder.ProjectDirectory, "startup-logcat.log"), timeout: 60
+				logcatFilePath: Path.Combine (Root, apkBuilder.ProjectDirectory, "startup-logcat.log"),
+				timeout: 60,
+				onMonitoringStarted: () => StartActivityAndAssert (proj)
 			),
 			$"Output did not contain {expectedLogcatOutput}!"
 		);