Increase code coverage!

[Datseris]

Here is the link to code coverage: https://app.codecov.io/gh/JuliaClimate/ClimateBase.jl

At the bottom of the page there is "Files". You can go there to see which files are missing tests. In fact if you click the files it tells you exactly which functions aren't used in the test suite.

Please do consider opening PRs that test more stuff!

Notice: I am using this package in scientific research extensively. It is "well tested" and accurate. I simply haven't written tests for everything yet, because I literally test the package in my science projects. So please don't be alarmed by the presence of this issue :D