1 files changed, 40 insertions, 0 deletions
diff --git a/src/test/common/test_counter.cc b/src/test/common/test_counter.cc
new file mode 100644
index 000000000..f9a7d6e6c
--- /dev/null
+++ b/src/test/common/test_counter.cc
@@ -0,0 +1,40 @@
+#include "common/DecayCounter.h"
+
+#include <gtest/gtest.h>
+
+#include <list>
+#include <cmath>
+
+TEST(DecayCounter, steady)
+{
+  static const double duration = 2.0;
+  static const double max = 2048.0;
+  static const double rate = 3.5;
+
+  DecayCounter d{DecayRate{rate}};
+  d.hit(max);
+  const auto start = DecayCounter::clock::now();
+  double total = 0.0;
+  while (1) {
+    const auto now = DecayCounter::clock::now();
+    auto el = std::chrono::duration<double>(now-start);
+    if (el.count() > duration) {
+      break;
+    }
+
+    double v = d.get();
+    double diff = max-v;
+    if (diff > 0.0) {
+      d.hit(diff);
+      total += diff;
+    }
+  }
+
+  /* Decay function: dN/dt = -λM where λ = ln(0.5)/rate
+   * (where M is the maximum value of the counter, not varying with time.)
+   * Integrating over t: N = -λMt (+c)
+   */
+  double expected = -1*std::log(0.5)/rate*max*duration;
+  std::cerr << "t " << total << " e " << expected << std::endl;
+  ASSERT_LT(std::abs(total-expected)/expected, 0.05);
+}