In Java, you can use PowerMock to mock or spy anything, even private static final things. I consider it a smell (though excessive mocking even without powermock is its own smell), but it's immensely valuable to get code you can't change (or fear changing because of its complexity and lack of tests, or simply don't have time to change because the refactoring would take a whole sprint) to have some tests.
You don't need interfaces for everything in order to do DI. Interfaces should be used only for having multiple implementations or to break dependency loops.
Other than that I'm in agreement, static methods generally aren't a good idea. They can all too easily balloon into big chunks of imperative code with inner dependencies (static or not) at 10 indentation levels deep. Non static methods can too, but not as easily, and you have more options for fixes/workarounds in those cases anyway. The only place they really make sense is as part of a set of pure primitive data transforms, and ought to be small.
In C# we have Moq that can mock normal classes, though it requires adding 'virtual' to every method you want to override which is a code smell too. In Java everything being virtual by default I guess it doesn't matter. We like to always keep an interface around as it gets the developer used to working that way and keeps the code consistent. Visual Studio provides a quick shortcut to auto gen the interface too.
You don't need interfaces for everything in order to do DI. Interfaces should be used only for having multiple implementations or to break dependency loops.
Other than that I'm in agreement, static methods generally aren't a good idea. They can all too easily balloon into big chunks of imperative code with inner dependencies (static or not) at 10 indentation levels deep. Non static methods can too, but not as easily, and you have more options for fixes/workarounds in those cases anyway. The only place they really make sense is as part of a set of pure primitive data transforms, and ought to be small.