Hi Masaya,
This can be taken easy using the EVM. You can order an EVM here:
http://www.ti.com/tool/tps650250evm-447
Please read this app note before you start testing. It discusses proper techniques for measuring efficiency.
http://www.ti.com/lit/an/slva236/slva236.pdf
Since, the TPS6502050 is a PMIC, you should also take a baseline input current measurement by measuring the input current with the DCDC converter disabled. Subtract that current from the recorded input currents as you measure the efficiency of the particular DCDC converter in question.