It's not necessarily recommended to mix stable and testing but it mostly works fine in my experience. I'd guess Gentoo gets around quite a few problems as every

It's not necessarily recommended to mix stable and testing but it mostly works fine in my experience. I'd guess Gentoo gets around quite a few problems as everything is compiled from source. So updating a single libary would cause a rebuild of everything that depends on it. Gentoo also has the concept of "Slots", so you could have multiple versions of the same libary installed and packages will choose their version to build against accordingly.