Developers who are familiar with the topic of clean code know that static methods are a problem, especially if it comes to testability. Static makes the code global, and if there is some kind of state involved it is even more a problem because this is global state then - both a maintenance and testability nightmare.
Unfortunately, sometimes you don't get around of using such code. This could be due to a third party library you have to use, or even because of limitations of PHP itself.
