As someone who has been out of Java for close to 10 years now, you certainly could do without Mockito, but you'd be writing a lot of boiler plate code repetitiv

As someone who has been out of Java for close to 10 years now, you certainly could do without Mockito, but you'd be writing a lot of boiler plate code repetitively. There's also the case of third-party libraries that you don't control and Mockito has decent facilities for working with those, especially when you're working with a codebase that isn't pure DI and interfaces.