diff --git a/message-queue/cpp/src/algorithm.cpp b/message-queue/cpp/src/algorithm.cpp
index dab6c4e..b5de1d2 100644
--- a/message-queue/cpp/src/algorithm.cpp
+++ b/message-queue/cpp/src/algorithm.cpp
@@ -22,7 +22,7 @@ optional<Results> FindMaximum(
 
   i = pow(2, i-1) + 1;
   for(auto n : ranges::views::iota(i)) {
-    auto opt = sample(i);
+    auto opt = sample(n);
     if (opt.has_value()) {
       auto rs = opt.value();
       if (prev.has_value() and rs.MessagesPerSecond <= prev.value().MessagesPerSecond)
diff --git a/message-queue/cpp/src/algorithm_unittest.cpp b/message-queue/cpp/src/algorithm_unittest.cpp
index ea1d856..ec41c6f 100644
--- a/message-queue/cpp/src/algorithm_unittest.cpp
+++ b/message-queue/cpp/src/algorithm_unittest.cpp
@@ -1,7 +1,55 @@
 #include <gtest/gtest.h>
 
+#include <optional>
+#include <list>
+
+#include "algorithm.hpp"
+#include "primitives.hpp"
+
+using namespace std;
+
+class Sampler {
+public:
+  list<int> calls;
+  optional<Results> operator()(int n) {
+    cout << "called with n=" << n << endl;
+    calls.push_back(n);
+    auto rs = Results();
+    switch(n) {
+      case 1:
+        rs.Add(WorkerResult(1, 1, chrono::duration<double>(1)));
+        break;
+      case 2:
+        rs.Add(WorkerResult(1, 2, chrono::duration<double>(1)));
+        break;
+      case 4:
+        rs.Add(WorkerResult(1, 3, chrono::duration<double>(1)));
+        break;
+      case 8:
+        rs.Add(WorkerResult(1, 2, chrono::duration<double>(1)));
+        break;
+      case 5:
+        rs.Add(WorkerResult(1, 4, chrono::duration<double>(1)));
+        break;
+      case 6:
+        rs.Add(WorkerResult(1, 3, chrono::duration<double>(1)));
+        break;
+      default:
+        stringstream ss;
+        ss << "Unexpected N=" << n;
+        throw runtime_error(ss.str());
+    }
+
+    return rs;
+  }
+};
+
 namespace {
 TEST(FindMaximumTest, Test) {
-  EXPECT_TRUE(true);
+  Sampler s;
+  auto rs = FindMaximum(ref(s));
+  ASSERT_EQ(rs.value().MessagesPerSecond, 4);
+  list<int> expected = {1, 2, 4, 8, 5, 6};
+  ASSERT_EQ(expected, s.calls);
 }
 }