I might not describe them exactly like that, but they aren't tightly focussed unit tests. I was basing this on the example of the recently merged LambertConformal PR #292 which has similar tests (see earlier review comments). They are aimed at testing the ability of cartopy to correctly project to TranverseMercator. I could have picked some points, but a geometry i.e. a coastline was a quick, thorough, albeit broad way to do it. The second aim is to test the parameters of the constructor i.e. passing the the parameters to the constructor does give the equivalent (except for limits) of an OSGB projection.