The pattern is `Test_<method>__<aspect/group>`. So in this case it's testing the `register` method, and it's focussing on the `CoordSig_general` aspects of that method. I take that to mean it's looking at merge errors from having cubes with different lists of coords (e.g. completely different names), rather than where two coords are similar but differ in some subtle aspect (e.g. point values).