How i can test the capacitor bank that improve P.F?

For testing the compansation performance of a PFI capacitor bank I suggest you the following methods

1 - By Use of AVO meter with FARADs measurement feature, to measure the capacitance (C) of each capacitor individually and compare your readings with the respective rated capacitonce writen on the capacitor label.

2- Use a power analyzer to measure the KVARs on the mian line to the cupacitor bank and compare your reading with the total KVARs of the ON stages at the time of reading. Or you can use the power/network analyzer to measure the KVAR of each stage when it is ON and compare the reading with KVAR of the respective stage.

3- OR, you can use the PF controller display and Keypad. Firstly switch off all stages and set the PF controller to the manual mode. Then Set the display to the KVAR reading. Take the KVAR reading when all stages are OFF just before swiching the stage to be test, then switch on the stage under test and take the KVAR reading and then compare the difference/reduction in KVAR and compare it to the KVAR of the respective stage. This last method could be less accurate as the KVAR of the load could vary unpredictably.

capacitor to compensate the phase angle between current and volt due to motor coil and soft starter

so we need capacitor bank with multiple stages 

to choose the needed value to get maximum P.F by eliminating this angle and get current and volt in the same phase (0 angle)