How 'testable' is Rust?

Hello! I would like to know the degree of testability of Rust, and factors that determine the testability, like the controllability, observability, isolateability, the separation of concerns, understandability and heterogeneity. Also, if there are any test statistics available. Thanks! :slight_smile:

This kind of question is better posed on http://users.rust-lang.org/, as this forum is specifically for coordinating Rust development, rather than talking about usage. Mind posting over there?