Serial Correlation and Covariance stationary are two different concepts and I also know that Covariance Stationary (or lack of it i.e. unit root) can be tested by Dickey Fuller Method.
That said, it looks to me from the EOC #3, and BB #12 and page-436 (section 4.1, 2nd last paragraph) of the curriculum that if looking at a time series plot, we see there is no strong trend or there is no persistence in the errors then it can be safely assumed that there is no serial correlation NOR is there is a unit root (i.e. the time series is covariance stationary)
Can somebody comment?