Run test tearDowns and clean up temporary directories when a signal is caught.

lib/src/frontend/expect.dart

Index: lib/src/frontend/expect.dart
diff --git a/lib/src/frontend/expect.dart b/lib/src/frontend/expect.dart
index 71a141694f42ba7f0a04415ca4f34651430672c0..d39986b40231df2599403430c43909ff703e40e5 100644
--- a/lib/src/frontend/expect.dart
+++ b/lib/src/frontend/expect.dart
@@ -6,6 +6,9 @@ library test.frontend.expect;
 
 import 'package:matcher/matcher.dart';
 
+import '../backend/closed_exception.dart';
+import '../backend/invoker.dart';
+
 /// An exception thrown when a test assertion fails.
 class TestFailure {
   final String message;
@@ -36,6 +39,8 @@ typedef String ErrorFormatter(
 /// [verbose] should be specified as `true`.
 void expect(actual, matcher,
     {String reason, bool verbose: false, ErrorFormatter formatter}) {
+  if (Invoker.current.closed) throw new ClosedException();
+
   matcher = wrapMatcher(matcher);
   var matchState = {};
   try {