ADD test for multi-tasking

common/speedometer.cpp

@@ -80,6 +80,10 @@ float Speedometer::getDistance() {
 }
 
 void Speedometer::reset() {
+#if defined(MBED_TEST_MODE)
+    _cbOnReset();
+#endif
+
     this->_totalDistanceMutex.lock();
     this->_totalDistance = 0.0f;
     this->_totalDistanceMutex.unlock();