Make JSON stringify throw a JsonUnsupportedObjectError on cycles.

tests/lib/json/json_test.dart

 // Copyright (c) 2011, 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.
 
 library json_tests;
-import "package:expect/expect.dart";
+import 'package:unittest/unittest.dart';
 import 'dart:json' as json;
-import 'dart:html';
-import '../../pkg/unittest/lib/unittest.dart';
-import '../../pkg/unittest/lib/html_config.dart';
 
 main() {
-  useHtmlConfiguration();
   test('Parse', () {
     // Scalars.
     expect(json.parse(' 5 '), equals(5));
     expect(json.parse(' -42 '), equals(-42));
     expect(json.parse(' 3e0 '), equals(3));
     expect(json.parse(' 3.14 '), equals(3.14));
     expect(json.parse('true '), isTrue);
     expect(json.parse(' false'), isFalse);
     expect(json.parse(' null '), isNull);
     expect(json.parse('\n\rnull\t'), isNull);
@@ skipping 87 matching lines @@
     validateRoundTrip({' hi bob ':3, '':4.5});
     validateRoundTrip(
         {'x':{'a':3, 'b':-4.5}, 'y':[{}], 'z':'hi', 'w':{'c':null, 'd':true},
                   'v':null});
 
     expect(json.stringify(new ToJson(4)), "4");
     expect(json.stringify(new ToJson([4, "a"])), '[4,"a"]');
     expect(json.stringify(new ToJson([4, new ToJson({"x":42})])),
            '[4,{"x":42}]');
 
-    Expect.throws(() {
+    expect(() {
       json.stringify([new ToJson(new ToJson(4))]);
-    });
+    }, throwsJsonError);
 
-    Expect.throws(() {
+    expect(() {
       json.stringify([new Object()]);
-    });
+    }, throwsJsonError);
 
   });
 
   test('stringify throws if argument cannot be converted', () {
     /**
      * Checks that we get an exception (rather than silently returning null) if
      * we try to stringify something that cannot be converted to json.
      */
-    expect(() => json.stringify(new TestClass()), throws);
+    expect(() => json.stringify(new TestClass()), throwsJsonError);
     });
   });
+
+  test('stringify throws if toJson throws', () {
+    expect(() => json.stringify(new ToJsoner("bad", throws: true)),
+           throwsJsonError);
+  });
+
+  test('stringify throws if toJson returns non-serializable value', () {
+    expect(() => json.stringify(new ToJsoner(new TestClass())),
+           throwsJsonError);
+  });
+
+  test('stringify throws on cyclic values', () {
+    var a = [];
+    var b = a;
+    for (int i = 0; i < 50; i++) {
+      b = [b];
+    }
+    a.add(b);
+    expect(() => json.stringify(a), throwsJsonError);
+  });
 }
 
 class TestClass {
   int x;
   String y;
 
   TestClass() : x = 3, y = 'joe' { }
 }
 
+class ToJsoner {
+  final Object returnValue;
+  final bool throws;
+  ToJsoner(this.returnValue, {this.throws});
+  Object toJson() {
+    if (throws) throw returnValue;
+    return returnValue;
+  }
+}
+
 class ToJson {
   final object;
   const ToJson(this.object);
   toJson() => object;
 }
 
+var throwsJsonError =
+    throwsA(new isInstanceOf<json.JsonUnsupportedObjectError>());
+
 /**
  * Checks that the argument can be converted to a JSON string and
  * back, and produce something equivalent to the argument.
  */
 validateRoundTrip(expected) {
   expect(json.parse(json.stringify(expected)), equals(expected));
 }
-
-