As a software engineer
I want to have good code coverage of ResolverService
So that I can have confidence that changes won't break existing functionality

Given mockall can be used to mock struct impl dependencies
When adding unit tests to ResolverService
Then create mockall mocks to create mock instances of ArchiveCachingClient, PointerCachingClient, RegisterCachingClient and PointerNameResolver
And use these mocks to test ResolverService methods
And use 'mock!' to define test doubles whose actions can be mocked
And use PointerService in pointer_service.rs and PointerCachingClient in pointer_caching_client.rs as examples

Implementation Notes

- Place any unit tests at the bottom of the same file as the associated production code
- Increment patch version of anttp package in Cargo.toml
- Create a copy of this issue description and save to /spec using the name of this issue as the filename (with lower underscore case, starting with the 5 char padded issue name, e.g. 00001_issue_title.txt)
- Fix failing unit tests in ResolverService and improve coverage