Python tests

[Rombur]

The following functions need to be tested:

• charge_discharge.py:
  • charge_mode = constant_power
  • discharge_mode = constant_current
  • discharge_mode = constant_voltage
  • discharge_mode = constant_load
  • CyclicChargeDischarge
• data_helpers.py:
  • plot_data
  • open_file_in_write_mode
• impedance_spectroscopy.py: plot_bode
• voltammetry.py: plot_cyclic_voltammogram