Provide better documentation/examples for `provideDummy`/`provideDummyBuilder` about mockito

[jamesderlin]

Additionally:

• https://stackoverflow.com/q/77272908/
• https://stackoverflow.com/q/77814642/
• https://stackoverflow.com/q/77993902/

[jamesderlin]

@DerJojo11 Let's say you have:

class Bar {}

class Foo {
  Bar method() => Bar();
}

and now you want to mock Foo. With @GenerateNiceMocks, the generated implementation for MockFoo needs method() to be able to return something. It can't return null since the return type is non-nullable. Normally code generation will generate something like class FakeBar extends Fake implements Bar {}, and then MockFoo's method implementation can construct and return a FakeBar instance.

However, if Bar is sealed, then it cannot be extended nor implemented, disallowing the generation of FakeBar. Therefore Mockito can't generate a default value for a Bar on its own, and it needs users to specify what default value to use.

[DerJojo11]

THANK YOU!

Struggled the last hour why and how I fix this error. Don't get why I have to do this now (freshly updated).

So I give a thumbs up to the question: why do we need this now?