What's the pattern name for wrapping access to static methods/variables?

Following on from the question How do the Proxy, Decorator, Adapter, and Bridge Patterns differ?, how would you describe the following pattern which I've needed to implement on several occasions?

The scenario is that I'm referencing a static method or variable from a third-party class, but I want to hide it behind an interface so that I can mock it for testing.

For example, in Java the commons-lang library has a SystemUtils class with constants IS_OS_WINDOWS etc. I want to run tests which are independent of the underlying OS and mimic various OSs, so I wrap access to the constant as follows:

interface ISystemUtils {
    boolean isOsWindows();
}

class SystemUtilsImpl implements ISystemUtils {
    @Override
    public boolean isOsWindows() {
        return SystemUtils.IS_OS_WINDOWS;
    }
}

Is this a Proxy, a generic "wrapper", or something else?