Fixed problem where multiple ticks within the same second causes task to expire multiple times that second.

libcron/Cron.h

@@ -68,6 +68,7 @@ namespace libcron
                     }
             };
 
+
             Queue tasks{};
             ClockType clock{};
             bool first_tick = true;
@@ -112,6 +113,21 @@ namespace libcron
     {
         size_t res = 0;
 
+        if(!first_tick)
+        {
+            // Only allow time to flow if at least one second has passed since the last tick,
+            // either forward or backward.
+            auto diff = now - last_tick;
+
+            constexpr auto one_second = std::chrono::seconds{1};
+
+            if(diff < one_second && diff > -one_second)
+            {
+                now = last_tick;
+            }
+        }
+
+
         if (first_tick)
         {
             first_tick = false;

test/CronTest.cpp

@@ -297,3 +297,41 @@ SCENARIO("Clock changes")
         }
     }
 }
+
+SCENARIO("Multiple ticks per second")
+{
+    Cron<TestClock> c{};
+    auto& clock = c.get_clock();
+
+    auto now = sys_days{2018_y / 05 / 05};
+    clock.set(now);
+
+    int run_count = 0;
+
+    // Every 10 seconds
+    REQUIRE(c.add_schedule("Clock change task", "*/10 0 * * * ?", [&run_count]()
+    {
+        run_count++;
+    })
+    );
+
+    c.tick(now);
+
+    REQUIRE(run_count == 1);
+
+    WHEN("Many ticks during one seconds")
+    {
+        for(auto i = 0; i < 10; ++i)
+        {
+            clock.add(std::chrono::microseconds{1});
+            c.tick();
+        }
+
+        THEN("Run count has not increased")
+        {
+            REQUIRE(run_count == 1);
+        }
+
+    }
+
+}