I don't see any mentions of spies support in Mockito for dart in the latest versions.
In the changelog:
2.0.0-dev # Remove export of spy and any dart:mirrors based API from mockito.dart. Users may import as package:mockito/mirrors.dart going forward. Deprecated mockito_no_mirrors.dart; replace with mockito.dart. Require Dart SDK >=1.21.0 <2.0.0 to use generic methods.
0.11.1 # Move the reflection-based spy code into a private source file. Now package:mockito/mockito.dart includes this reflection-based API, and a new package:mockito/mockito_no_mirrors.dart doesn't require mirrors.
0.10.0 # Added support for spy.
Is there any support for spies in the context of unit-testing in Dart?
