  Several methods proposed to measure the angle $\gamma$ in the KM unitarity
triangle assumed that the tree contribution to $B^-\to \pi^-\bar K^0 $ is
purely due to annihilation contributions and is negligibly small. This
assumption has to be tested in order to have a correct interpretation of the
experimental data. In this paper we show that using SU(3) symmetry, the
smallness of the tree contribution can be tested in a dynamic model independent
way. We also derive several relations between CP violating rate differences for
$B\to P P$ decays without assuming the smallness of the annihilation
contributions. These relations provide important tests for the Standard Model
of CP violation.
