[tools] add PoissonNextSend method that returns mockable time

src/net.h

@@ -943,11 +943,13 @@ public:
     void MaybeSetAddrName(const std::string& addrNameIn);
 };
 
-
-
-
-
 /** Return a timestamp in the future (in microseconds) for exponentially distributed events. */
 int64_t PoissonNextSend(int64_t now, int average_interval_seconds);
 
+/** Wrapper to return mockable type */
+inline std::chrono::microseconds PoissonNextSend(std::chrono::microseconds now, std::chrono::seconds average_interval)
+{
+    return std::chrono::microseconds{PoissonNextSend(now.count(), average_interval.count())};
+}
+
 #endif // BITCOIN_NET_H

src/test/net_tests.cpp

@@ -303,5 +303,19 @@ BOOST_AUTO_TEST_CASE(LocalAddress_BasicLifecycle)
     BOOST_CHECK_EQUAL(IsLocal(addr), false);
 }
 
+BOOST_AUTO_TEST_CASE(PoissonNextSend)
+{
+    g_mock_deterministic_tests = true;
+
+    int64_t now = 5000;
+    int average_interval_seconds = 600;
+
+    auto poisson = ::PoissonNextSend(now, average_interval_seconds);
+    std::chrono::microseconds poisson_chrono = ::PoissonNextSend(std::chrono::microseconds{now}, std::chrono::seconds{average_interval_seconds});
+
+    BOOST_CHECK_EQUAL(poisson, poisson_chrono.count());
+
+    g_mock_deterministic_tests = false;
+}
 
 BOOST_AUTO_TEST_SUITE_END()