Importing selenium works without any issue in Python 2x but you'll see error while working in Python 3x. I'm guessing since you have both Python 2 and 3 both installed, it checks for selenium installation while running installation test and returns ok because of version 2.
I would suggest you to uninstall all python environments and then only install python 3.
For selenium download the package from
]selenium-3.141.0.tar.gz, unpack and install manually.
For your reference, You can extract the file using these commands.
tar -xvzf selenium-3.141.0.tar.gz
and install it.
python setup.py install
This should solve your problem.