Refactoring Code with Static Dependencies for Testability

Methods that have dependencies on static methods can be difficult to test. In this example we have a dependency that we obtain via a static method that we do not have control over and we want to test the surrounding code.

public void myMethod(Long id) {
     // ...
     Dependency dependency = DependencyUtil.getDependency();
     // ...
 }

We can refactor this to:

public void myMethod(Long id) {
     Dependency dependency = DependencyUtil.getDependency();
     myMethod(dependency);
 }

 void myMethod(Long id, Dependency dependency) {
     // ...
     doSomething(dependency);
     // ...
 }

We overload the method signature and preserve the public API. We make the new method have default access to make it testable. We can now mock Dependency however we like.