Migrated test block 26 to Dart 2.0.

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));
-    testShuffle(new Int32List(size)..setAll(0, numbers));
-    testShuffle(new Uint16List(size)..setAll(0, numbers));
-    testShuffle(new Int16List(size)..setAll(0, numbers));
-    // Some numbers will be truncated in the following two.
-    testShuffle(new Uint8List(size)..setAll(0, numbers));
-    testShuffle(new Int8List(size)..setAll(0, numbers));
-    testShuffle(numbers.map((x) => "$x").toList());
-  }
-
-  // Check that it actually can keep the same list (regression test).
-  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,
-  // without considering order.
-  Map seen = {};
-  for (var e in list) {
-    seen[e] = seen.putIfAbsent(e, () => 0) + 1;
-  }
-  for (var e in copy) {
-    int remaining = seen[e];
-    remaining -= 1; // Throws if e was not in map at all.
-    if (remaining == 0) {
-      seen.remove(e);
-    } else {
-      seen[e] = remaining;
-    }
-  }
-  Expect.isTrue(seen.isEmpty);
-  // Test that shuffle actually does make a change. Repeat until the probability
-  // of a proper shuffling hitting the same list again is less than 10^80
-  // (arbitrary bignum - approx. number of atoms in the universe).
-  //
-  // The probablility of shuffling a list of length n into the same list is
-  // 1/n!. If one shuffle didn't change the list, repeat shuffling until
-  // probability of randomly hitting the same list every time is less than
-  // 1/1e80.
-
-  bool listsDifferent() {
-    for (int i = 0; i < list.length; i++) {
-      if (list[i] != copy[i]) return true;
-    }
-    return false;
-  }
-
-  if (list.length < 59) {
-    // 59! > 1e80.
-    double limit = 1e80;
-    double fact = 1.0;
-    for (int i = 2; i < list.length; i++) fact *= i;
-    double combos = fact;
-
-    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 get _next {
-    int next = _values[index];
-    index = (index + 1) % _values.length;
-    return next;
-  }
-
-  int nextInt(int limit) => _next % limit;
-
-  double nextDouble() => _next / 256.0;
-
-  bool nextBool() => _next.isEven;
-}