Tracking issue for RFC 2471, "Add lint warning for inner function marked as `#[test]`"

[Centril]

This is a tracking issue for the RFC "Add lint warning for inner function marked as #[test]" (rust-lang/rfcs#2471).

Steps:

• Implement the RFC
• Is there anything left to do?

Unresolved questions:

None

[Centril]

@estebank is there anything left to do here or should we just close the issue?

[estebank]

I believe we can close this as is. The linked PR was all needed to satisfy the RFC as it stands.