Make List.shuffle take an optional Random object to use.

tests/corelib/shuffle_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.
 
 // Dart test for List.shuffle.
 library shuffle_test;
 import "dart:typed_data";
+import "dart:math" show Random;
 import "package:expect/expect.dart";
 
 main() {
   List mkList(int n) => new List.generate(n, (x) => x);
 
   for (int size in [0, 1, 2, 3, 7, 15, 99, 1023]) {
     List numbers = new List.generate(size, (x) => x);
     testShuffle(numbers.toList(growable: true));
     testShuffle(numbers.toList(growable: false));
     testShuffle(new Uint32List(size)..setAll(0, numbers));
@@ skipping 10 matching lines @@
   List l = [1, 2];
   success: {
     for (int i = 0; i < 266; i++) {
       int first = l.first;
       l.shuffle();
       if (l.first == first) break success;  // List didn't change.
     }
     // Chance of changing 266 times in a row should be < 1:1e80.
     Expect.fail("List changes every time.");
   }
+
+  testRandom();
 }
 
 void testShuffle(list) {
   List copy = list.toList();
   list.shuffle();
   if (list.length < 2) {
     Expect.listEquals(copy, list);
     return;
   }
   // Test that the list after shuffling has the same elements as before,
@@ skipping 35 matching lines @@
 
     while (!listsDifferent() && combos < limit) {
       list.shuffle();
       combos *= fact;
     }
   }
   if (!listsDifferent()) {
     Expect.fail("Didn't shuffle at all, p < 1:1e80: $list");
   }
 }
+
+
+// Checks that the "random" argument to shuffle is used.
+testRandom() {
+  List randomNums = [37, 87, 42, 157, 252, 17];
+  List numbers = new List.generate(25, (x) => x);
+  List l1 = numbers.toList()..shuffle(new MockRandom(randomNums));
+  for (int i = 0; i < 50; i++) {
+    // With same random sequence, we get the same shuffling each time.
+    List l2 = numbers.toList()..shuffle(new MockRandom(randomNums));
+    Expect.listEquals(l1, l2);
+  }
+}
+
+class MockRandom implements Random {
+  final List<int> _values;
+  int index = 0;
+  MockRandom(this._values);
+
+  int nextInt(int limit) {
+    int next = _values[index];
+    index = (index + 1) % _values.length;
+    return next % limit;
+  }
+
+  double nextDouble() {
+    int next = _values[index];
+    index = (index + 1) % _values.length;
+    return next / 256.0;
+  }
+
+  bool nextBool() {
+    int next = _values[index];
+    index = (index + 1) % _values.length;
+    return next.isEven;
+  }
+}

[bakster, 2013/10/04 11:19:34]

Please refactor:
  int _next() => _values[index++ % _values.length];   
  int nextInt(int limit) => _next() % limit;
  double nextDouble()  => _next() / 256.0;
  bool nextBool() => _next().isEven;