How can I inject mocks into spring security classes

I am using @PreAuthorize to secure a web request

@PreAuthorize("(@assessmentAuthService.canViewAssessment(#id))")

AssessmentAuthService is created automatically by spring, but I need to inject a mock object into it from my unity test.

private final AssessmentService assessmentService;

@Inject
public AssessmentAuthorizationServiceImpl(AssessmentService assessmentService) {
    this.assessmentService = assessmentService;
}

This is because I want assessmentService.getById(assessmentId) to return a mocked object.