For navigating between parallel directory structures (src/ and test/), I made an awful hack called c-, that sed subs src/ for test/ and vice versa on pwd. A fluke grade.
When actually inside vim Tim Pope's excellent vim-projectionist has a wonderfully useful feature for flipping between various related files(:h projectionist-alternate). The whole plugin is really cool, it makes it so simple to configure project specific working environments with it.
https://github.com/tpope/vim-projectionist