Hello, Everyone.
I am working on a pooled OLS, after executing xttest0. Then I conducted diagnostic tests:
regress $ylist $xlist , vce(cluster id)
estat vif
estat ovtest

all of these tests gave me expected results, except for
Wooldridge test for autocorrelation, xtserial $ylist $xlist

Stata gave me:

. xtserial $ylist $xlist

Wooldridge test for autocorrelation in panel data
H0: no first-order autocorrelation
F( 1, 16) = 1432.673
Prob > F = 0.0000

Thank you.