- Implement comprehensive tests for RelationshipManager covering various relationship types (BelongsTo, HasMany, HasOne, ManyToMany) and eager loading functionality. - Include caching mechanisms and error handling in RelationshipManager tests. - Create unit tests for ShardManager to validate shard creation, routing, management, global index operations, and query functionalities. - Ensure tests cover different sharding strategies (hash, range, user) and handle edge cases like errors and non-existent models.