  The Hubble parameter is a critical measurement in cosmology, which contains
the most direct information of the cosmic expansion history. Since discrepancy
is found between low redshift and high redshift estimations of Hubble constant,
we are interested in whether that tension indicates dynamical dark energy. In
this paper we emphasize that the observed Hubble parameters at various
redshifts, along with observed Hubble constant, can help us in probing the
evolutional behavior of the mysterious dark energy. Null hypothesis tests are
carried out with two diagnostic approaches. We find out that, according to the
present measurements of Hubble parameters, rejection of constant dark energy is
captured at $1\sigma$ level from null tests with and without the observed value
of Hubble constant.
