Record/replay test infrastructure. (#8597)

This adds the test harness for record/replay tests.

packages/flutter_tools/lib/executable.dart

@@ -146,8 +146,8 @@ Future<int> run(List<String> args, List<FlutterCommand> subCommands, {
       await _exit(0);
       runCompleter.complete(0);
     }, onError: (dynamic error, Chain chain) {
-      flutterVersion ??= FlutterVersion.getVersionString();
-      _handleToolError(error, chain, verbose, args, reportCrashes, flutterVersion)
+      String getVersion() => flutterVersion ?? FlutterVersion.getVersionString();
+      _handleToolError(error, chain, verbose, args, reportCrashes, getVersion)
           .then(runCompleter.complete, onError: runCompleter.completeError);
     });
     return runCompleter.future;
@@ -160,7 +160,7 @@ Future<int> _handleToolError(
     bool verbose,
     List<String> args,
     bool reportCrashes,
-    String flutterVersion,
+    String getFlutterVersion(),
 ) async {
   if (error is UsageException) {
     stderr.writeln(error.message);
@@ -208,7 +208,7 @@ Future<int> _handleToolError(
       await CrashReportSender.instance.sendReport(
         error: error,
         stackTrace: chain,
-        flutterVersion: flutterVersion,
+        flutterVersion: getFlutterVersion(),
       );
       try {
         final File file = await _createLocalCrashReport(args, error, chain);

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

@@ -166,6 +166,13 @@ class BufferLogger extends Logger {
     printStatus(message);
     return new Status();
   }
+
+  /// Clears all buffers.
+  void clear() {
+    _error.clear();
+    _status.clear();
+    _trace.clear();
+  }
 }
 
 class VerboseLogger extends Logger {

packages/flutter_tools/test/replay/common.dart

+// Copyright 2015 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 'dart:async';
+
+import 'package:flutter_tools/executable.dart' as tools;
+import 'package:flutter_tools/src/base/io.dart';
+import 'package:test/test.dart';
+
+import '../src/common.dart';
+import '../src/context.dart';
+
+/// Runs the specified [testMethod] in a minimal `AppContext` that is set up
+/// to redirect log output to a `BufferLogger` to avoid spamming `stdout`.
+///
+/// Test methods will generally want to use [expectProcessExits] in their method
+/// bodies.
+void testReplay(
+  String description,
+  dynamic testMethod(), {
+  Timeout timeout,
+  Map<Type, Generator> overrides: const <Type, Generator>{},
+  bool skip,
+}) {
+  setUp(() {
+    setExitFunctionForTests();
+  });
+
+  tearDown(() {
+    restoreExitFunction();
+  });
+
+  testUsingContext(
+    description,
+    testMethod,
+    timeout: timeout,
+    overrides: overrides,
+    skip: skip,
+    initializeContext: (_) {},
+  );
+}
+
+/// Expects that the specified [command] to Flutter tools exits with the
+/// specified [exitCode] (defaults to zero). It is expected that callers will
+/// be running in a test via [testReplay].
+///
+/// [command] should be the list of arguments that are passed to the `flutter`
+/// command-line tool.  For example:
+///
+/// ```
+///   <String>[
+///     'run',
+///     '--no-hot',
+///     '--no-resident',
+///   ]
+/// ```
+void expectProcessExits(List<String> command, {dynamic exitCode: 0}) {
+  final Future<Null> mainFuture = tools.main(command);
+  expect(mainFuture, throwsProcessExit(exitCode));
+}

packages/flutter_tools/test/src/context.dart

@@ -74,7 +74,7 @@ void testUsingContext(String description, dynamic testMethod(), {
     final String flutterRoot = getFlutterRoot();
 
     try {
-      return await testContext.runInZone(() {
+      return await testContext.runInZone(() async {
         // Apply the overrides to the test context in the zone since their
         // instantiation may reference items already stored on the context.
         overrides.forEach((Type type, dynamic value()) {
@@ -83,23 +83,28 @@ void testUsingContext(String description, dynamic testMethod(), {
         // Provide a sane default for the flutterRoot directory. Individual
         // tests can override this.
         Cache.flutterRoot = flutterRoot;
-        return testMethod();
+        return await testMethod();
+      }, onError: (dynamic error, StackTrace stackTrace) {
+        _printBufferedErrors(testContext);
+        throw error;
       });
     } catch (error) {
-      if (testContext[Logger] is BufferLogger) {
-        final BufferLogger bufferLogger = testContext[Logger];
-        if (bufferLogger.errorText.isNotEmpty)
-          print(bufferLogger.errorText);
-      }
-      // Previously the following line read "throw error;". This is bad because
-      // it drops the error's actual stacktrace. Use 'rethrow' to preserve
-      // the stacktrace.
+      _printBufferedErrors(testContext);
       rethrow;
     }
 
   }, timeout: timeout, skip: skip);
 }
 
+void _printBufferedErrors(AppContext testContext) {
+  if (testContext[Logger] is BufferLogger) {
+    final BufferLogger bufferLogger = testContext[Logger];
+    if (bufferLogger.errorText.isNotEmpty)
+      print(bufferLogger.errorText);
+    bufferLogger.clear();
+  }
+}
+
 String getFlutterRoot() {
   Error invalidScript() => new StateError('Invalid script: ${platform.script}');