Add a 'secure' constructor to Random in dart:math returning a cryptographically

tests/lib/math/random_secure_test.dart

+// Copyright (c) 2015, 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.
+
+// Test that the secure random generator does not systematically generates
+// duplicates. Note that this test is flaky by definition, since duplicates
+// can occur. They should be extremely rare, though.
+
+// Library tag to allow Dartium to run the test.
+library random_secure;
+
+import "package:expect/expect.dart";
+import 'dart:math';
+
+main() {
+  var results;
+  var rng0;
+  var rng1;
+  var checkInt = (max) {
+    var intVal0 = rng0.nextInt(max);
+    var intVal1 = rng1.nextInt(max);
+    if (max > (1 << 28)) {
+      Expect.isFalse(results.contains(intVal0));
+      results.add(intVal0);
+      Expect.isFalse(results.contains(intVal1));
+      results.add(intVal1);
+    }
+  };
+  results = [];
+  rng0 = new Random.secure();
+  for(var i = 0; i <= 32; i++) {
+    rng1 = new Random.secure();
+    checkInt(1 << 32);
+    checkInt(1 << (32 - i));

[Lasse Reichstein Nielsen, 2015/10/15 09:32:33]

Does it even make sense to call for i < (1<<28) - the checkInt doesn't check
anything in that case.

[regis, 2015/10/15 17:12:02]

It makes sure that we can generate random values with a large max without
crashing or looping forever.

+    checkInt(1000000000);
+  }
+  var checkDouble = () {
+    var doubleVal0 = rng0.nextDouble();
+    var doubleVal1 = rng1.nextDouble();
+    Expect.isFalse(results.contains(doubleVal0));
+    results.add(doubleVal0);
+    Expect.isFalse(results.contains(doubleVal1));
+    results.add(doubleVal1);
+  };
+  results = [];
+  rng0 = new Random.secure();
+  for(var i = 0; i < 32; i++) {
+    rng1 = new Random.secure();

[Lasse Reichstein Nielsen, 2015/10/15 09:32:33]

You could just make checkDouble create the new rng1 as a local variable.

[regis, 2015/10/15 17:12:02]

Sure. I prefer to keep the symmetry with other tests.

+    checkDouble();
+  }
+  var cnt0 = 0;
+  var cnt1 = 0;
+  rng0 = new Random.secure();
+  for(var i = 0; i < 32; i++) {
+    rng1 = new Random.secure();
+    cnt0 += rng0.nextBool() ? 1 : 0;
+    cnt1 += rng1.nextBool() ? 1 : 0;
+  }
+  Expect.isTrue((cnt0 > 0) && (cnt0 < 32));
+  Expect.isTrue((cnt1 > 0) && (cnt1 < 32));
+}
+