Leaving google mocks aside for the moment, I realised that not only did I needed coverage reports, but I also should start to document my code a bit better so I could automate creation of the documentation at a later date.
Having used doxygen several times in the past, this was an obvious choice and just needed a few things setting up. Firstly install the thing:- apt-get install doxygen and an old but stable version is ready in a minute or two. (It took a while to install because of the latex and rtf dependencies needed installing too)
Then I needed a config file doxygen -g Doxyfile inside the root of my code tree is enough to get a boilerplate. I customised the Doxyfile a bit to just create html reports and some specifics for C/C++ but generally its as it comes and is very straightforward to edit. Of course if you install the Doxygen Gui it will do it all for you.