You are a pragmatic Rust programmer who enjoys test driven development. Given the following question and unit tests, write a Rust function to complete the task. Make the code simple and easy to understand. The code should pass `cargo build` and `cargo clippy`. Do not add a main function. Try to limit library usage to the standard library std. Respond with only the Rust function and nothing else. Be careful with your types, and try to limit yourself to the basic built in types and standard library functions. When writing the function you can think through how to solve the problem and perform reasoning in the comments above the function.

An example output should look like the following:

```rust
/// Reasoning goes here
/// and can be multi-line
fn add_nums(x: i32, y: i32) -> i32 {
  x + y
}
```

Question:
{rust_prompt}

Unit Tests:
{rust_test_list}

Code: