Be more consistent about how stack traces are output from flutter_test (#9361)

dev/automated_tests/flutter_test/exception_handling_expectation.txt

+[^═]*(this line contains the test framework's output with the clock and so forth)?
+══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
+The following message was thrown running a test:
+Who lives, who dies, who tells your story\?
+
+When the exception was thrown, this was the stack:
+#0      main.<anonymous closure> \(.+[/\\]dev[/\\]automated_tests[/\\]flutter_test[/\\]exception_handling_test\.dart:10:5\)
+<asynchronous suspension>
+#1      .+ \(package:flutter_test[/\\]src[/\\]widget_tester\.dart:[0-9]+:[0-9]+\)
+<<skip until matching line>>
+^\(elided [0-9]+ .+[^)]$
+^.+\)$
+
+The test description was:
+Exception handling in test harness - string
+════════════════════════════════════════════════════════════════════════════════════════════════════
+.*(this line has more of the test framework's output)?
+  Test failed\. See exception logs above\.
+ *
+[^═]*(this line contains the test framework's output with the clock and so forth)?
+══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
+The following assertion was thrown running a test:
+Who lives, who dies, who tells your story\?
+
+When the exception was thrown, this was the stack:
+#0      main.<anonymous closure> \(.+[/\\]dev[/\\]automated_tests[/\\]flutter_test[/\\]exception_handling_test\.dart:13:5\)
+<asynchronous suspension>
+#1      .+ \(package:flutter_test[/\\]src[/\\]widget_tester\.dart:[0-9]+:[0-9]+\)
+<<skip until matching line>>
+^\(elided [0-9]+ .+[^)]$
+^.+\)$
+
+The test description was:
+Exception handling in test harness - FlutterError
+════════════════════════════════════════════════════════════════════════════════════════════════════
+.*(this line has more of the test framework's output)?
+  Test failed\. See exception logs above\.
+ *
+[^═]*(this line contains the test framework's output with the clock and so forth)?
+══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
+The following message was thrown running a test:
+Who lives, who dies, who tells your story\?
+
+When the exception was thrown, this was the stack:
+#[0-9]+ +main.<anonymous closure> \(.+[/\\]dev[/\\]automated_tests[/\\]flutter_test[/\\]exception_handling_test\.dart:16:9\)
+#[0-9]+ +main.<anonymous closure> \(.+[/\\]dev[/\\]automated_tests[/\\]flutter_test[/\\]exception_handling_test\.dart:15:105\)
+#[0-9]+ +.+ \(package:flutter_test[/\\]src[/\\]widget_tester\.dart:[0-9]+:[0-9]+\)
+<<skip until matching line>>
+^\(elided [0-9]+ .+[^)]$
+^.+\)$
+
+The test description was:
+Exception handling in test harness - uncaught Future error
+════════════════════════════════════════════════════════════════════════════════════════════════════
+.*(this line has more of the test framework's output)?
+  Test failed\. See exception logs above\.
+ *
+.*..:.. \+0 -3: Some tests failed\. *

dev/automated_tests/flutter_test/exception_handling_test.dart

+// Copyright 2017 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:flutter/foundation.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('Exception handling in test harness - string', (WidgetTester tester) async {
+    throw 'Who lives, who dies, who tells your story?';
+  });
+  testWidgets('Exception handling in test harness - FlutterError', (WidgetTester tester) async {
+    throw new FlutterError('Who lives, who dies, who tells your story?');
+  });
+  testWidgets('Exception handling in test harness - uncaught Future error', (WidgetTester tester) async {
+    new Future<Null>.error('Who lives, who dies, who tells your story?');
+  });
+}

packages/flutter_test/lib/src/binding.dart

@@ -18,6 +18,7 @@ import 'package:meta/meta.dart';
 import 'package:quiver/testing/async.dart';
 import 'package:quiver/time.dart';
 import 'package:test/test.dart' as test_package;
+import 'package:stack_trace/stack_trace.dart' as stack_trace;
 import 'package:vector_math/vector_math_64.dart';
 
 import 'stack_manipulation.dart';
@@ -353,7 +354,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
           // will see them in the logs at some point.
           FlutterError.dumpErrorToConsole(new FlutterErrorDetails(
             exception: exception,
-            stack: stack,
+            stack: _unmangle(stack),
             context: 'running a test (but after the test had completed)',
             library: 'Flutter test framework'
           ), forceReport: true);
@@ -394,7 +395,7 @@ abstract class TestWidgetsFlutterBinding extends BindingBase
         final int stackLinesToOmit = reportExpectCall(stack, expectLine);
         FlutterError.reportError(new FlutterErrorDetails(
           exception: exception,
-          stack: stack,
+          stack: _unmangle(stack),
           context: 'running a test',
           library: 'Flutter test framework',
           stackFilter: (Iterable<String> frames) {
@@ -1021,3 +1022,11 @@ class _EmptyStack implements StackTrace {
   @override
   String toString() => '';
 }
+
+StackTrace _unmangle(StackTrace stack) {
+  if (stack is stack_trace.Trace)
+    return stack.vmTrace;
+  if (stack is stack_trace.Chain)
+    return stack.toTrace().vmTrace;
+  return stack;
+}

packages/flutter_test/pubspec.yaml

@@ -9,3 +9,8 @@ dependencies:
 
   flutter:
     sdk: flutter
+
+  # We import stack_trace because the test packages uses it and we
+  # need to be able to unmangle the stack traces that it passed to
+  # stack_trace. See https://github.com/dart-lang/test/issues/590
+  stack_trace: any # use version expected by test package

packages/flutter_tools/test/test_test.dart

@@ -23,6 +23,11 @@ void main() {
     final String automatedTestsDirectory = fs.path.join('..', '..', 'dev', 'automated_tests');
     final String flutterTestDirectory = fs.path.join(automatedTestsDirectory, 'flutter_test');
 
+    testUsingContext('Exception handling in test harness', () async {
+      Cache.flutterRoot = '../..';
+      return _testFile('exception_handling', automatedTestsDirectory, flutterTestDirectory);
+    });
+
     testUsingContext('TestAsyncUtils guarded function test', () async {
       Cache.flutterRoot = '../..';
       return _testFile('test_async_utils_guarded', automatedTestsDirectory, flutterTestDirectory);