Add tests to core for nested dependency injection

[ben-ryder]

Package Information: core @ 2*

Describe your feature
Add unit tests for nested/recursive dependency injection.

For example if DependencyA is registered to the DI system and it requires DependencyB which requires DependencyC then DependencyB and DependencyC should also be registered to the DI system and the instance of DependencyA should be passed the correct instance of those dependencies (depending on the injection mode).

Is your suggestion related to any problems?
This is a critical part of the DI system that currently has no test coverage.

Additional context
n/a