1 files changed, 61 insertions, 0 deletions
diff --git a/mfbt/tests/TestRandomNum.cpp b/mfbt/tests/TestRandomNum.cpp
new file mode 100644
index 0000000000..f53c42fc83
--- /dev/null
+++ b/mfbt/tests/TestRandomNum.cpp
@@ -0,0 +1,61 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "mozilla/RandomNum.h"
+#include <vector>
+
+/*
+
+ * We're going to check that random number generation is sane on a basic
+ * level - That is, we want to check that the function returns success
+ * and doesn't just keep returning the same number.
+ *
+ * Note that there are many more tests that could be done, but to really test
+ * a PRNG we'd probably need to generate a large set of randoms and
+ * perform statistical analysis on them. Maybe that's worth doing eventually?
+ *
+ * For now we should be fine just performing a dumb test of generating 5
+ * numbers and making sure they're all unique. In theory, it is possible for
+ * this test to report a false negative, but with 5 numbers the probability
+ * is less than one-in-a-trillion.
+ *
+ */
+
+#define NUM_RANDOMS_TO_GENERATE 5
+
+using mozilla::Maybe;
+using mozilla::RandomUint64;
+
+static uint64_t getRandomUint64OrDie() {
+  Maybe<uint64_t> maybeRandomNum = RandomUint64();
+
+  MOZ_RELEASE_ASSERT(maybeRandomNum.isSome());
+
+  return maybeRandomNum.value();
+}
+
+static void TestRandomUint64() {
+  // The allocator uses RandomNum.h too, but its initialization path allocates
+  // memory. While the allocator itself handles the situation, we can't, so
+  // we make sure to use an allocation before getting a Random number ourselves.
+  std::vector<uint64_t> randomsList;
+  randomsList.reserve(NUM_RANDOMS_TO_GENERATE);
+
+  for (uint8_t i = 0; i < NUM_RANDOMS_TO_GENERATE; ++i) {
+    uint64_t randomNum = getRandomUint64OrDie();
+
+    for (uint64_t num : randomsList) {
+      MOZ_RELEASE_ASSERT(randomNum != num);
+    }
+
+    randomsList.push_back(randomNum);
+  }
+}
+
+int main() {
+  TestRandomUint64();
+  return 0;
+}