Make service tests more resilient to isolate load timing

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';
@@ skipping 297 matching lines @@
           for (var test in vmTests) {
             vm.verbose = verbose_vm;
             print('Running $name [$testIndex/$totalTests]');
             testIndex++;
             await test(vm);
           }
         }
 
         // Run isolate tests.
         if (isolateTests != null) {
-          var isolate = await vm.isolates.first.load();
+          var isolate = await getFirstIsolate(vm);
           var testIndex = 1;
           var totalTests = isolateTests.length;
           for (var test in isolateTests) {
             vm.verbose = verbose_vm;
             print('Running $name [$testIndex/$totalTests]');
             testIndex++;
             await test(isolate);
           }
         }
 
         print('All service tests completed successfully.');
         testsDone = true;
         await process.requestExit();
       }, onError: (error, stackTrace) {
         if (testsDone) {
           print('Ignoring late exception during process exit:\n'
                 '$error\n#stackTrace');
         } else {
           process.requestExit();
           print('Unexpected exception in service tests: $error\n$stackTrace');
           throw error;
         }
       });
     });
   }
+
+
+
+  Future<Isolate> getFirstIsolate(WebSocketVM vm) async {
+    if (vm.isolates.isNotEmpty) {
+      var isolate = await vm.isolates.first.load();
+      if (isolate is Isolate) {
+        return isolate;
+      }
+    }
+
+    Completer completer = new Completer();
+    vm.getEventStream(VM.kIsolateStream).then((stream) {
+      var subscription;
+      subscription = stream.listen((ServiceEvent event) async {
+        if (completer == null) {
+          subscription.cancel();
+          return;
+        }
+        if (event.kind == ServiceEvent.kIsolateRunnable) {
+          if (vm.isolates.isNotEmpty) {
+            vm.isolates.first.load().then((result) {
+              if (result is Isolate) {
+                subscription.cancel();
+                completer.complete(result);
+                completer = null;
+              }
+            });
+          }
+        }
+      });
+    });
+
+    // The isolate may have started before we subscribed.
+    if (vm.isolates.isNotEmpty) {
+      vm.isolates.first.reload().then((result) async {
+        if (completer != null && result is Isolate) {
+          completer.complete(result);
+          completer = null;
+        }
+      });
+    }
+    return await completer.future;
+  }
 }
 
 /// 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 runIsolateTests(List<String> mainArgs,
                        List<IsolateTest> tests,
                        {testeeBefore(),
                         testeeConcurrent(),
@@ skipping 83 matching lines @@
     new _ServiceTesterRunner().run(
         mainArgs: mainArgs,
         extraArgs: extraArgs,
         vmTests: tests,
         pause_on_start: pause_on_start,
         pause_on_exit: pause_on_exit,
         verbose_vm: verbose_vm,
         pause_on_unhandled_exceptions: pause_on_unhandled_exceptions);
   }
 }