test charge for electrostatic potential

[vga_fh]

The manual states that VASP also calculates the average electrostatic potential at each ion, which is evaluated by placing a test charge with the norm 1 at each ion and calculating the volume integral.

My question is: Is the test charge positively charged (+1), like the definition of electrostatic potential, or negatively charged (-1), like CP2K (the electrons and the nuclei felt by a point charge with charge −e).

Any clarifications are greatly appreciated!