Module proptest

Property-based testing framework for Rust.

proptest is a property-based testing framework inspired by QuickCheck and Hypothesis. Instead of writing tests with specific hardcoded inputs, proptest generates many random test inputs to verify that properties of your code hold across a wide range of cases.

The crate automatically generates test data using Strategy types, runs tests with the proptest! macro, and when tests fail it shrinks the failing input to find the minimal test case that reproduces the failure. This helps discover edge cases and boundary conditions that might not be obvious from example-based testing.

Key features include strategies for generating primitives, collections, and custom types, the prop_assert! family of assertion macros, and automatic test case shrinking to minimal failing examples.

Proptest integrates with Rust's standard test harness and works alongside regular unit tests. It's particularly useful for testing functions with complex input spaces, validating invariants, and ensuring code behaves correctly across edge cases.

Examples

Basic property test verifying that reversing a vector twice returns the original:

use proptest::prelude::*;

proptest! {
    #[test]
    fn test_double_reverse(v: Vec<i32>) {
        let reversed_twice: Vec<_> = v.iter().cloned().rev().rev().collect();
        prop_assert_eq!(v, reversed_twice);
    }
}

Testing that addition is commutative:

use proptest::prelude::*;

proptest! {
    #[test]
    fn test_addition_commutative(a: i32, b: i32) {
        let sum1 = a.saturating_add(b);
        let sum2 = b.saturating_add(a);
        prop_assert_eq!(sum1, sum2);
    }
}

Using custom strategies to generate constrained data:

use proptest::prelude::*;

proptest! {
    #[test]
    fn test_positive_division(a in 1..1000i32, b in 1..1000i32) {
        let result = a / b;
        prop_assert!(result >= 0);
        prop_assert!(result <= a);
    }
}

Modules

Macros