Use --trace-service to help diagnose flaky tests.

runtime/observatory/tests/service/test_helper.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library test_helper;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 bool _isWebSocketDisconnect(e) {
   return e is NetworkRpcException;
 }
 
 // This invocation should set up the state being tested.
 const String _TESTEE_MODE_FLAG = "--testee-mode";
 
 class _TestLauncher {
   Process process;
   final List<String> args;
   bool killedByTester = false;
 
   _TestLauncher() : args = ['--enable-vm-service:0',
                             Platform.script.toFilePath(),
                             _TESTEE_MODE_FLAG] {}
 
-  Future<int> launch(bool pause_on_start, bool pause_on_exit) {
+  Future<int> launch(bool pause_on_start, bool pause_on_exit, bool trace_service) {
+    assert(pause_on_start != null);
+    assert(pause_on_exit != null);
+    assert(trace_service != null);
     String dartExecutable = Platform.executable;
     var fullArgs = [];
-    if (pause_on_start == true) {
+    if (trace_service) {
+      fullArgs.add('--trace-service');
+    }
+    if (pause_on_start) {
       fullArgs.add('--pause-isolates-on-start');
     }
-    if (pause_on_exit == true) {
+    if (pause_on_exit) {
       fullArgs.add('--pause-isolates-on-exit');
     }
     fullArgs.addAll(Platform.executableArguments);
     fullArgs.addAll(args);
     print('** Launching $dartExecutable ${fullArgs.join(' ')}');
     return Process.start(dartExecutable, fullArgs).then((p) {
 
       Completer completer = new Completer();
       process = p;
       var portNumber;
@@ skipping 49 matching lines @@
 
 /// Runs [tests] in sequence, each of which should take an [Isolate] and
 /// return a [Future]. Code for setting up state can run before and/or
 /// concurrently with the tests. Uses [mainArgs] to determine whether
 /// to run tests or testee in this invokation of the script.
 void runIsolateTests(List<String> mainArgs,
                      List<IsolateTest> tests,
                      {void testeeBefore(),
                       void testeeConcurrent(),
                       bool pause_on_start: false,
-                      bool pause_on_exit: false}) {
+                      bool pause_on_exit: false,
+                      bool trace_service: false}) {
   assert(!pause_on_start || testeeBefore == null);
   if (mainArgs.contains(_TESTEE_MODE_FLAG)) {
     if (!pause_on_start) {
       if (testeeBefore != null) {
         testeeBefore();
       }
       print(''); // Print blank line to signal that we are ready.
     }
     if (testeeConcurrent != null) {
       testeeConcurrent();
     }
     if (!pause_on_exit) {
       // Wait around for the process to be killed.
       stdin.first.then((_) => exit(0));
     }
   } else {
     var process = new _TestLauncher();
-    process.launch(pause_on_start, pause_on_exit).then((port) {
+    process.launch(pause_on_start, pause_on_exit, trace_service).then((port) {
       if (mainArgs.contains("--gdb")) {
         port = 8181;
       }
       String addr = 'ws://localhost:$port/ws';
       serviceHttpAddress = 'http://localhost:$port';
       var testIndex = 1;
       var totalTests = tests.length;
       var name = Platform.script.pathSegments.last;
       runZoned(() {
         new WebSocketVM(new WebSocketVMTarget(addr)).load()
@@ skipping 136 matching lines @@
 
 /// Runs [tests] in sequence, each of which should take an [Isolate] and
 /// return a [Future]. Code for setting up state can run before and/or
 /// concurrently with the tests. Uses [mainArgs] to determine whether
 /// to run tests or testee in this invokation of the script.
 Future runVMTests(List<String> mainArgs,
                   List<VMTest> tests,
                   {Future testeeBefore(),
                    Future testeeConcurrent(),
                    bool pause_on_start: false,
-                   bool pause_on_exit: false}) async {
+                   bool pause_on_exit: false,
+                   bool trace_service: false}) async {
   if (mainArgs.contains(_TESTEE_MODE_FLAG)) {
     if (!pause_on_start) {
       if (testeeBefore != null) {
         await testeeBefore();
       }
       print(''); // Print blank line to signal that we are ready.
     }
     if (testeeConcurrent != null) {
       await testeeConcurrent();
     }
     if (!pause_on_exit) {
       // Wait around for the process to be killed.
       stdin.first.then((_) => exit(0));
     }
   } else {
     var process = new _TestLauncher();
-    process.launch(pause_on_start, pause_on_exit).then((port) async {
+    process.launch(pause_on_start,
+                   pause_on_exit,
+                   trace_service).then((port) async {
       if (mainArgs.contains("--gdb")) {
         port = 8181;
       }
       String addr = 'ws://localhost:$port/ws';
       serviceHttpAddress = 'http://localhost:$port';
       var testIndex = 1;
       var totalTests = tests.length;
       var name = Platform.script.pathSegments.last;
       runZoned(() {
         new WebSocketVM(new WebSocketVMTarget(addr)).load()
             .then((VM vm) => Future.forEach(tests, (test) {
               print('Running $name [$testIndex/$totalTests]');
               testIndex++;
               return test(vm);
             })).then((_) => process.requestExit());
       }, onError: (e, st) {
         process.requestExit();
         if (!_isWebSocketDisconnect(e)) {
           print('Unexpected exception in service tests: $e $st');
           throw e;
         }
       });
     });
   }
 }