Add tests for nested contexts (#7197)

This tests against the failure that was fixed in #7189

packages/flutter_tools/lib/executable.dart

@@ -94,7 +94,7 @@ Future<Null> main(List<String> args) async {
   AppContext _executableContext = new AppContext();
 
   // Make the context current.
-  _executableContext.runInZone(() {
+  await _executableContext.runInZone(() {
     // Initialize the context with some defaults.
     // NOTE: Similar lists also exist in `bin/fuchsia_builder.dart` and
     // `test/src/context.dart`. If you update this list of defaults, look

packages/flutter_tools/lib/src/base/context.dart

@@ -59,7 +59,7 @@ class AppContext {
         : parentContext;
   }
 
-  dynamic runInZone(dynamic method(), {
+  Future<dynamic> runInZone(dynamic method(), {
     ZoneBinaryCallback<dynamic, dynamic, StackTrace> onError
   }) {
     return runZoned(
@@ -69,7 +69,7 @@ class AppContext {
     );
   }
 
-  dynamic _run(dynamic method()) async {
+  Future<dynamic> _run(dynamic method()) async {
     Zone previousZone = _zone;
     try {
       _zone = Zone.current;

packages/flutter_tools/test/context_test.dart

@@ -8,7 +8,7 @@ import 'package:flutter_tools/src/globals.dart';
 import 'package:test/test.dart';
 
 void main() {
-  group('DeviceManager', () {
+  group('AppContext', () {
     test('error', () async {
       AppContext context = new AppContext();
       BufferLogger mockLogger = new BufferLogger();
@@ -50,5 +50,31 @@ void main() {
       expect(mockLogger.statusText, '');
       expect(mockLogger.traceText, 'foo bar\n');
     });
+
+    test('awaitNestedZones', () async {
+      AppContext outerContext = new AppContext();
+      await outerContext.runInZone(() async {
+        AppContext middleContext = new AppContext();
+        await middleContext.runInZone(() async {
+          AppContext innerContext = new AppContext();
+          await innerContext.runInZone(() async {
+            expect(innerContext.getVariable(String), isNull);
+          });
+        });
+      });
+    });
+
+    test('fireAndForgetNestedZones', () async {
+      AppContext outerContext = new AppContext();
+      outerContext.runInZone(() async {
+        AppContext middleContext = new AppContext();
+        middleContext.runInZone(() async {
+          AppContext innerContext = new AppContext();
+          innerContext.runInZone(() async {
+            expect(innerContext.getVariable(String), isNull);
+          });
+        });
+      });
+    });
   });
 }