Coverage is computed in a nightly teamcity build. This coverage ignores any automatically generated files such as protocol buffers as well as binaries that aren't necessary for running cockroach. For more info see the coverage ignore file list.
You can view the coverage results at codecov.io/gh/cockroachdb/cockroach or coveralls.io/github/cockroachdb/cockroach.
Note: If a test fails no coverage is generated for that package which can lead to inconsistent coverage results from day to day.