  It was shown that the tension between the mass-squared differences obtained
from solar neutrinos and those acquired through KamLAND experiments may be
solved by the introduction of a non-standard flavor-dependent interaction (NSI)
in neutrino propagation. In this study, we discuss the possibility of testing
such a hypothesis using the future long-baseline neutrino experiments T2HKK and
DUNE. Assuming that the NSI does not exist, we provide the excluded region
within the ($\epsilon_D$, $\epsilon_N$) plane, where $\epsilon_D$ and
$\epsilon_N$ are the parameters appearing in the solar neutrino analysis
conducted with the NSI. We find that the best-fit value from the solar neutrino
and KamLAND data (global analysis of a particular coupling to quarks) can be
tested at more than 10$\sigma$ (3$\sigma$) by these two experiments for most of
the parameter space.
