spring attempt to inject #Autowired dependencies in a Mocked instance - testing

Question

I have the following classes:
com.foo.pkgx:
#Component public class A {}
#Component public class B {
#Autowired A a;
}
com.foo.pkgy:
#Component public class C {
#Autowired B b;
}
I.E. dependency-wise: C -> B -> A
When executing the following spock Specification:
#Configuration
#ComponentScan(basePackages = ["com.foo.pkgy"])
class Config {
def mockFactory = new DetachedMockFactory()
#Bean
B b() {mockFactory.Mock(B)};
}
#ContextConfiguration(classes = Config)
class CSpec extends Specification {
#Autowired
C c;
def "sanity"() {
expect: c
}
}
The test fails initialization:
Caused by: org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'c':
Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException:
Could not autowire field: com.foo.pkgx.B com.foo.pkgy.C.b;
nested exception is org.springframework.beans.factory.BeanCreationException:
Error creating bean with name 'b':
Injection of autowired dependencies failed;
nested exception is org.springframework.beans.factory.BeanCreationException:
Could not autowire field: com.foo.pkgx.A com.foo.pkgx.B.a;
nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException:
No qualifying bean of type [com.foo.pkgx.A] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {#org.springframework.beans.factory.annotation.Autowired(required=true)}
I read this as "tried to wire A into B, but failed". I wasn't expecting B to undergo autowiring, as it is mocked.
Could someone shed some light?
Thanks!

Answer 1

Mock of a class is a subclass generated by code-generation library, byte-buddy or cglib-nodep to name a few. It's a regular bean from Spring perspective. And once any bean is instantiated then at some point, Spring starts "introspection" of the bean by means of various ...BeanPostProcessors. E.g. Autowiring is handled by AutowiredAnnotationBeanPostProcessor. This postprocessor works in such a way that each bean is inspected through the entire class hierarchy. So your class B is there with #Autowired field A and Spring tries to resolve this dependency with no luck.
The good news, however, is that there is a demand for such a feature of disabling autowiring on a per-bean basis. And looks like eventually, Spring team will introduce it soon.
Meanwhile you can just mock A so that B's dependency is resolved. Or you can just use interfaces for your components, instead of using just classes. I believe the latter is the best practice