Adding to a closed sink throws.

tests/standalone/io/file_test.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 //
 // Dart test program for testing file I/O.
 
 // OtherResources=empty_file
 // OtherResources=file_test.txt
 // OtherResources=fixed_length_file
 // OtherResources=read_as_text.dat
@@ skipping 970 matching lines @@
   }
 
   // Tests stream exception handling after file was closed.
   static void testCloseExceptionStream() {
     asyncTestStarted();
     List<int> buffer = new List<int>(42);
     File file = new File(tempDirectory.path + "/out_close_exception_stream");
     file.createSync();
     var output = file.openWrite();
     output.close();
-    output.add(buffer); // Ignored.
+    Expect.throws(() {
+      output.add(buffer);
+    });
     output.done.then((_) {
       file.deleteSync();
       asyncTestDone("testCloseExceptionStream");
     });
   }
 
   // Tests buffer out of bounds exception.
   static void testBufferOutOfBoundsException() {
     bool exceptionCaught = false;
     bool wrongExceptionCaught = false;
@@ skipping 673 matching lines @@
       testSetLastAccessedSyncDirectory();
       testDoubleAsyncOperation();
       asyncEnd();
     });
   }
 }
 
 main() {
   FileTest.testMain();
 }