Andrew, I suspect that this is failing the second test because the new plot lines are being plotted over the previous plot (from test 1). It is always a good practice to use 'hold off' (here and in MATLAB, generally) to ensure that a new figure is created for the next plot. Having said that, I will consider adding a 'figure' command to the tests, since Cody does not display the plots and it is difficult to debug this particular problem without seeing the plots.