does “adb install”overwrite or skips when the apk is already installed?

i just want to have more clarity in what adb does by default .

when i run adb install for an apk that is already installed the cmd only shows :

Performing Streamed Install

it does not specify if it is skipping the install or if overwriting.

and is there a verbose option for adb for it to be more clear of what is doing ?