rust assert!

`assert!` is a macro provided by the Rust standard library that is used for testing and debugging purposes. It takes a boolean expression as its argument and checks if the expression evaluates to true. If the expression is false, the macro will panic and print an error message.

Here's an example usage of `assert!`:

fn add(a: i32, b: i32) -> i32 {
    a + b
}

fn main() {
    assert!(add(2, 2) == 4);
}

In this example, `assert!` is used to test the `add` function. The macro checks if the result of `add(2, 2)` is equal to `4`. If the result is not equal to `4`, the macro will panic and print an error message.

`assert!` is commonly used in unit tests to ensure that the code behaves as expected. It's also useful for debugging purposes, as it can help identify unexpected behavior in the code.