For testing OSes is irrelevant. Only the browser and its version.
PS: I was wrong. It is clear that the design of the OS will be different due to fonts, components, therefore, believed that the OS should only bother the designers. Always had a thing with the page functionality. But the fact that in IE with the same version, but different OS can run blocks
, was news to me. This is serious design. Now it is necessary to record not only the list of browsers and OS for a specific version.