## Cargo.toml

```toml
[package]
name = "sum_two_numbers"
version = "0.1.0"
edition = "2021"

[dependencies]

## src/lib.rs

```rust
fn solution(a: i32, b: i32) -> i32 {
    a + b
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_solution() {
        assert_eq!(solution(1, 2), 3);
        assert_eq!(solution(-1, 1), 0);
        assert_eq!(solution(0, 0), 0);
    }
}

```

## Build

```bash
cargo build --tests
```

## Test

```bash
cargo test
```



**Explanation:**

* **Cargo.toml:**  This file defines the project metadata like name, version, and dependencies. In this case, we have a simple project without external dependencies.

* **src/lib.rs:** This file contains our code:
    * `solution` function: Takes two integers (`a` and `b`) and returns their sum.
    * `tests` module (using the `#[cfg(test)]` attribute):  This module is only compiled when running tests. It contains the `test_solution` function that uses assertions (`assert_eq!`) to verify if the `solution` function returns the expected values for different inputs.

* **Build:** The `cargo build --tests` command compiles both the main code and the test code.  The `--tests` flag ensures that tests are built alongside the regular project.

* **Test:** The `cargo test` command executes all the tests defined in the `tests` module. You'll see output indicating whether each test passed or failed.