added test and comments
diff --git a/aos/common/time_test.cc b/aos/common/time_test.cc
index 678c013..e6b7bb0 100644
--- a/aos/common/time_test.cc
+++ b/aos/common/time_test.cc
@@ -116,6 +116,10 @@
   EXPECT_EQ(sysClkRateGet() / 100,
             MACRO_DARG(Time(0, Time::kNSecInSec / 100).ToTicks()));
 }
+TEST(TimeTest, InTicks) {
+  EXPECT_EQ(MACRO_DARG(Time(2, Time::kNSecInSec)),
+            Time::InTicks(sysClkRateGet() * 2.5));
+}
 #endif
 
 TEST(TimeTest, InMS) {