If tracking has already started, calls to start or stop should raise exceptions informing the user that the tracking for this tracker object has already completed i.e. 'Cannot start tracking since tracking has stopped' and 'Cannot stop tracking since tracking has already stopped'.
If tracking has already started, calls to start or stop should raise exceptions informing the user that the tracking for this tracker object has already completed i.e. 'Cannot start tracking since tracking has stopped' and 'Cannot stop tracking since tracking has already stopped'.