gem spec: where do you specify dependencies that's useful in both runtime and development environments

Question

If I understand correctly,

spec.add_runtime_dependency "something"

is for runtime dependencies.

spec.add_development_dependency "something"

is for development dependencies.

What about dependencies that's useful in both runtime and development environments, where do they go?

Answer 1

Runtime dependencies are what your gem needs to work (such as rails needing activesupport, or faker called by you own class).

Development dependencies are useful for when someone wants to make modifications to your gem (such as rspec)

There is not another option. Can you provide a use case example?