1 files changed, 39 insertions, 0 deletions
diff --git a/src/test/test_weighted_shuffle.cc b/src/test/test_weighted_shuffle.cc
new file mode 100644
index 000000000..9f92cbdc0
--- /dev/null
+++ b/src/test/test_weighted_shuffle.cc
@@ -0,0 +1,39 @@
+// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
+// vim: ts=8 sw=2 smarttab
+
+#include "common/weighted_shuffle.h"
+#include <array>
+#include <map>
+#include "gtest/gtest.h"
+
+TEST(WeightedShuffle, Basic) {
+  std::array<char, 5> choices{'a', 'b', 'c', 'd', 'e'};
+  std::array<int, 5> weights{100, 50, 25, 10, 1};
+  std::map<char, std::array<unsigned, 5>> frequency {
+    {'a', {0, 0, 0, 0, 0}},
+    {'b', {0, 0, 0, 0, 0}},
+    {'c', {0, 0, 0, 0, 0}},
+    {'d', {0, 0, 0, 0, 0}},
+    {'e', {0, 0, 0, 0, 0}}
+  }; // count each element appearing in each position
+  const int samples = 10000;
+  std::random_device rd;
+  for (auto i = 0; i < samples; i++) {
+    weighted_shuffle(begin(choices), end(choices),
+		     begin(weights), end(weights),
+		     std::mt19937{rd()});
+    for (size_t j = 0; j < choices.size(); ++j)
+      ++frequency[choices[j]][j];
+  }
+  // verify that the probability that the nth choice is selected as the first
+  // one is the nth weight divided by the sum of all weights
+  const auto total_weight = std::accumulate(weights.begin(), weights.end(), 0);
+  constexpr float epsilon = 0.02;
+  for (unsigned i = 0; i < choices.size(); i++) {
+    const auto& f = frequency[choices[i]];
+    const auto& w = weights[i];
+    ASSERT_NEAR(float(w) / total_weight,
+		float(f.front()) / samples,
+		epsilon);
+  }
+}