How do you test classes that use Singleton or static instances?

Testing singletons/statics is tricky due to global state. Best practices include:

• Refactor to use interfaces and DI instead of static/singletons.
• Wrap static calls behind interfaces so you can mock them.
• Use specialized mocking tools (e.g., Microsoft Fakes) if refactoring isn't possible.
• Avoid static state to improve testability.