When releasing 0.20.0 and 0.20.1, we encountered unexpected failures on MacOS, so maybe we should run tests on MacOS here.
Comments from @ogrisel :
To avoid this in the future we should run macOS tests on master. It used to be the case that travis macOS workers would tend to be saturated for a significant fraction of the time with a large backlog of pending jobs. However this does not seem to have been a significant problem over the last month: https://www.traviscistatus.com/#month Alternatively we could configure CI on azure pipelines that offers free CI for linux, macOS and windows with the same configuration file.