On the other hand layers of defaults are tedious

Perhaps Transformation::Encryption should not have any defaults. Those
would be left to the top-level EncryptionMapper.

Right now we kind of need the same test on two levels for the same
default set on each of those levels. Which makes sense from one
perspective.
From the other I'd like to cut down those combinations on
next breaking-API-release (not sure if Transformation::Encryption is
public interface though...)

Author: mostlyobvious

ruby_event_store/.mutant.yml

@@ -28,3 +28,4 @@ matcher:
    - RubyEventStore::Mappers::EncryptionKey#ciphertext_from_authenticated
    - RubyEventStore::Mappers::JSONMapper#initialize
    - RubyEventStore::Serializers::YAML.load
+   - RubyEventStore::Mappers::EncryptionMapper#initialize