There is no Network Testing Companion PSGallery package. Packages don't normally have spaces so most likely you were looking for NetworkTestingCompanion which also doesn't exist in the PSGallery.
Interestingly enough however you can google and it will find such a package in the PSGallery here. But it doesn't show up when searching which leads me to believe it is either not published or it is simply a module file and hence cannot be imported directly.
I would recommend you simply copy the .psm1 file and place it in your local PS modules and use it directly rather than trying to get it from PSGallery. I'm not sure where you heard about this package but I would recommend you contact the source and let them know about it as I don't know how to contact the author on PSGallery directly.