Add some basic tests for evaluating expressions in `flutter test` (#24513)

* Add some basic tests for evaluating expressions in `flutter test`

* Review tweaks

packages/flutter_tools/test/integration/expression_evaluation_test.dart

@@ -11,6 +11,7 @@ import 'package:vm_service_lib/vm_service_lib.dart';
 
 import '../src/common.dart';
 import 'test_data/basic_project.dart';
+import 'test_data/tests_project.dart';
 import 'test_driver.dart';
 import 'test_utils.dart';
 
@@ -79,6 +80,47 @@ void main() {
       await evaluateComplexReturningExpressions(_flutter);
     });
   }, timeout: const Timeout.factor(6));
+
+  group('flutter test expression evaluation', () {
+    Directory tempDir;
+    final TestsProject _project = TestsProject();
+    FlutterTestTestDriver _flutter;
+
+    setUp(() async {
+      tempDir = createResolvedTempDirectorySync();
+      await _project.setUpIn(tempDir);
+      _flutter = FlutterTestTestDriver(tempDir);
+    });
+
+    tearDown(() async {
+      await _flutter.quit();
+      tryToDelete(tempDir);
+    });
+
+    test('can evaluate trivial expressions in a test', () async {
+      await _flutter.test(
+        withDebugger: true,
+        beforeStart: () => _flutter.addBreakpoint(_project.breakpointUri, _project.breakpointLine),
+      );
+      await evaluateTrivialExpressions(_flutter);
+    });
+
+    test('can evaluate complex expressions in a test', () async {
+      await _flutter.test(
+        withDebugger: true,
+        beforeStart: () => _flutter.addBreakpoint(_project.breakpointUri, _project.breakpointLine),
+      );
+      await evaluateComplexExpressions(_flutter);
+    });
+
+    test('can evaluate expressions returning complex objects in a test', () async {
+      await _flutter.test(
+        withDebugger: true,
+        beforeStart: () => _flutter.addBreakpoint(_project.breakpointUri, _project.breakpointLine),
+      );
+      await evaluateComplexReturningExpressions(_flutter);
+    });
+  }, timeout: const Timeout.factor(6));
 }
 
 Future<void> evaluateTrivialExpressions(FlutterTestDriver flutter) async {

packages/flutter_tools/test/integration/test_data/tests_project.dart

+// Copyright 2018 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+
+import 'package:file/file.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+
+import '../test_utils.dart';
+import 'project.dart';
+
+class TestsProject extends Project {
+  @override
+  final String pubspec = '''
+  name: test
+  environment:
+    sdk: ">=2.0.0-dev.68.0 <3.0.0"
+
+  dependencies:
+    flutter:
+      sdk: flutter
+
+  dev_dependencies:
+    flutter_test:
+      sdk: flutter
+  ''';
+
+  @override
+  String get main => '// Unused';
+
+  final String testContent = r'''
+  import 'package:flutter_test/flutter_test.dart';
+
+  void main() {
+    testWidgets('Hello world test', (WidgetTester tester) async {
+      expect(true, isTrue); // BREAKPOINT
+    });
+  }
+  ''';
+
+  @override
+  Future<void> setUpIn(Directory dir) {
+    this.dir = dir;
+    writeFile(testFilePath, testContent);
+    return super.setUpIn(dir);
+  }
+
+  String get testFilePath => fs.path.join(dir.path, 'test', 'test.dart');
+
+  @override
+  Uri get breakpointUri => Uri.file(testFilePath);
+
+  @override
+  int get breakpointLine => lineContaining(main, '// BREAKPOINT');
+}

packages/flutter_tools/test/integration/test_driver.dart

@@ -55,6 +55,7 @@ abstract class FlutterTestDriver {
 
   Future<void> _setupProcess(
     List<String> args, {
+    String script,
     bool withDebugger = false,
     bool pauseOnExceptions = false,
     File pidFile,
@@ -66,6 +67,9 @@ abstract class FlutterTestDriver {
     if (pidFile != null) {
         args.addAll(<String>['--pid-file', pidFile.path]);
     }
+    if (script != null) {
+      args.add(script);
+    }
     _debugPrint('Spawning flutter $args in ${_projectFolder.path}');
 
     const ProcessManager _processManager = LocalProcessManager();
@@ -93,6 +97,32 @@ abstract class FlutterTestDriver {
     _stderr.stream.listen(_debugPrint);
   }
 
+  Future<void> connectToVmService({bool pauseOnExceptions = false}) async {
+    _vmService = await vmServiceConnectUri(_vmServiceWsUri.toString());
+      _vmService.onSend.listen((String s) => _debugPrint('==> $s'));
+      _vmService.onReceive.listen((String s) => _debugPrint('<== $s'));
+      await Future.wait(<Future<Success>>[
+        _vmService.streamListen('Isolate'),
+        _vmService.streamListen('Debug'),
+      ]);
+
+      // On hot restarts, the isolate ID we have for the Flutter thread will
+      // exit so we need to invalidate our cached ID.
+      _vmService.onIsolateEvent.listen((Event event) {
+        if (event.kind == EventKind.kIsolateExit && event.isolate.id == _flutterIsolateId) {
+          _flutterIsolateId = null;
+        }
+      });
+
+      // Because we start paused, resume so the app is in a "running" state as
+      // expected by tests. Tests will reload/restart as required if they need
+      // to hit breakpoints, etc.
+      await waitForPause();
+      if (pauseOnExceptions) {
+        await _vmService.setExceptionPauseMode(await _getFlutterIsolateId(), ExceptionPauseMode.kUnhandled);
+      }
+  }
+
   Future<int> quit() => _killGracefully();
 
   Future<int> _killGracefully() async {
@@ -326,12 +356,14 @@ class FlutterRunTestDriver extends FlutterTestDriver {
   @override
   Future<void> _setupProcess(
     List<String> args, {
+    String script,
     bool withDebugger = false,
     bool pauseOnExceptions = false,
     File pidFile,
   }) async {
     await super._setupProcess(
       args,
+      script: script,
       withDebugger: withDebugger,
       pauseOnExceptions: pauseOnExceptions,
       pidFile: pidFile,
@@ -353,30 +385,7 @@ class FlutterRunTestDriver extends FlutterTestDriver {
           timeout: appStartTimeout);
       final String wsUriString = debugPort['params']['wsUri'];
       _vmServiceWsUri = Uri.parse(wsUriString);
-      _vmService =
-          await vmServiceConnectUri(_vmServiceWsUri.toString());
-      _vmService.onSend.listen((String s) => _debugPrint('==> $s'));
-      _vmService.onReceive.listen((String s) => _debugPrint('<== $s'));
-      await Future.wait(<Future<Success>>[
-        _vmService.streamListen('Isolate'),
-        _vmService.streamListen('Debug'),
-      ]);
-
-      // On hot restarts, the isolate ID we have for the Flutter thread will
-      // exit so we need to invalidate our cached ID.
-      _vmService.onIsolateEvent.listen((Event event) {
-        if (event.kind == EventKind.kIsolateExit && event.isolate.id == _flutterIsolateId) {
-          _flutterIsolateId = null;
-        }
-      });
-
-      // Because we start paused, resume so the app is in a "running" state as
-      // expected by tests. Tests will reload/restart as required if they need
-      // to hit breakpoints, etc.
-      await waitForPause();
-      if (pauseOnExceptions) {
-        await _vmService.setExceptionPauseMode(await _getFlutterIsolateId(), ExceptionPauseMode.kUnhandled);
-      }
+      await connectToVmService(pauseOnExceptions: pauseOnExceptions);
       await resume(wait: false);
     }
 
@@ -496,6 +505,81 @@ class FlutterRunTestDriver extends FlutterTestDriver {
   }
 }
 
+class FlutterTestTestDriver extends FlutterTestDriver {
+  FlutterTestTestDriver(Directory _projectFolder, {String logPrefix}):
+    super(_projectFolder, logPrefix: logPrefix);
+
+  Future<void> test({
+    String testFile = 'test/test.dart',
+    bool withDebugger = false,
+    bool pauseOnExceptions = false,
+    File pidFile,
+    Future<void> Function() beforeStart,
+  }) async {
+    await _setupProcess(<String>[
+        'test',
+        '--machine',
+        '-d',
+        'flutter-tester'
+    ], script: testFile, withDebugger: withDebugger, pauseOnExceptions: pauseOnExceptions, pidFile: pidFile);
+  }
+
+  @override
+  Future<void> _setupProcess(
+    List<String> args, {
+    String script,
+    bool withDebugger = false,
+    bool pauseOnExceptions = false,
+    File pidFile,
+    Future<void> Function() beforeStart,
+  }) async {
+    await super._setupProcess(
+      args,
+      script: script,
+      withDebugger: withDebugger,
+      pauseOnExceptions: pauseOnExceptions,
+      pidFile: pidFile,
+    );
+
+    // Stash the PID so that we can terminate the VM more reliably than using
+    // _proc.kill() (because _proc is a shell, because `flutter` is a shell
+    // script).
+    final Map<String, dynamic> version = await _waitForJson();
+    _procPid = version['pid'];
+
+    if (withDebugger) {
+      final Map<String, dynamic> startedProcess = await _waitFor(event: 'test.startedProcess', timeout: appStartTimeout);
+      final String vmServiceHttpString = startedProcess['params']['observatoryUri'];
+      _vmServiceWsUri = Uri.parse(vmServiceHttpString).replace(scheme: 'ws', path: '/ws');
+      await connectToVmService(pauseOnExceptions: pauseOnExceptions);
+      // Allow us to run code before we start, eg. to set up breakpoints.
+      if (beforeStart != null) {
+        await beforeStart();
+      }
+      await resume(wait: false);
+    }
+  }
+
+  Future<Map<String, dynamic>> _waitForJson({
+    Duration timeout,
+  }) async {
+    return _timeoutWithMessages<Map<String, dynamic>>(
+      () => _stdout.stream.map<Map<String, dynamic>>(_parseJsonResponse).first,
+      timeout: timeout,
+      message: 'Did not receive any JSON.',
+    );
+  }
+
+  Map<String, dynamic> _parseJsonResponse(String line) {
+    try {
+      return json.decode(line);
+    } catch (e) {
+      // Not valid JSON, so likely some other output.
+      return null;
+    }
+  }
+}
+
 Stream<String> transformToLines(Stream<List<int>> byteStream) {
   return byteStream.transform<String>(utf8.decoder).transform<String>(const LineSplitter());
 }