How to Write Property-Based Tests in Rust (proptest, quickcheck)

Use the proptest crate to define a test function that takes arbitrary inputs and asserts a property holds for all generated values. Add proptest to your Cargo.toml dependencies, import the proptest macro, and define a test function that takes arguments matching the property you want to verify.

use proptest::prelude::*;

proptest! {
    #[test]
    fn addition_is_commutative(a: i32, b: i32) {
        prop_assert_eq!(a + b, b + a);
    }
}

Run the test with cargo test to automatically generate thousands of random inputs and verify the property.

Property-based testing automatically generates thousands of random inputs to check if a rule always holds true, rather than testing specific examples. It is like checking if a bridge can hold any weight by dropping random objects on it, instead of just testing with one specific car. You use this when you need to ensure your code handles edge cases and unexpected inputs without manually writing every possible test case.