Syntax prohibits assignment in assert.

tests/corelib/iterable_generate_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.
 
 
 import "package:expect/expect.dart";
 
 main() {
   bool checkedMode = false;
-  assert(checkedMode = true);
+  assert((checkedMode = true));
   void test(expectedList, generatedIterable) {
     Expect.equals(expectedList.length, generatedIterable.length);
     Expect.listEquals(expectedList, generatedIterable.toList());
   }
   test([], new Iterable.generate(0));
   test([0], new Iterable.generate(1));
   test([0,1,2,3,4], new Iterable.generate(5));
   test(["0","1","2","3","4"], new Iterable.generate(5, (x) => "$x"));
   test([2,3,4,5,6], new Iterable.generate(7).skip(2));
   test([0,1,2,3,4], new Iterable.generate(7).take(5));
@@ skipping 15 matching lines @@
   Expect.isTrue(st is Iterable<String>);
   Expect.isTrue(st.iterator is Iterator<String>);
   Expect.isFalse(st is Iterable<int>);
   Expect.isFalse(st.iterator is Iterator<int>);
   test(["0","1","2","3","4"], st);
 
   if (checkedMode) {
     Expect.throws(() => new Iterable<String>.generate(5));
   }
 }