Configuring the number of tests cases required

The default number of successful test cases that must execute for a test as a whole to pass is currently 256. If you are not satisfied with this and want to run more or fewer, there are a few ways to do this.

The first way is to set the environment-variable PROPTEST_CASES to a value that can be successfully parsed as a u32. The value you set to this variable is now the new default. (This only applies when the std feature of proptest is enabled, which it is by default.)

Another way is to use #![proptest_config(expr)] inside proptest! where expr : Config. To only change the number of test cases, you can simply write:

extern crate proptest;
use proptest::prelude::*;

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

proptest! {
    // The next line modifies the number of tests.
    fn dummy(a in 0..1) {} // Doctests don't build `#[test]` functions, so we need this
    fn test_add(a in 0..1000i32, b in 0..1000i32) {
        let sum = add(a, b);
        assert!(sum >= a);
        assert!(sum >= b);
fn main() {

Through the same proptest_config mechanism you may fine-tune your configuration through the Config type. See its documentation for more information.