third_party/rust_crates/vendor/proptest/examples/fib.rs

//-
// Copyright 2018 Jason Lingle
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

// This #[cfg] is only here so that CI can test building proptest with the
// timeout feature disabled. You do not need it in your code.
#[cfg(feature = "timeout")]
mod fib {
    use proptest::prelude::*;

    // The worst possible way to calculate Fibonacci numbers
    fn fib(n: u64) -> u64 {
        if n <= 1 {
            n
        } else {
            fib(n - 1) + fib(n - 2)
        }
    }

    proptest! {
        #![proptest_config(ProptestConfig {
            // Setting both fork and timeout is redundant since timeout implies
            // fork, but both are shown for clarity.
            fork: true,
            timeout: 1000,
            .. ProptestConfig::default()
        })]

        // NB We omit #[test] on the test function so that main() can call it.
        fn test_fib(n in prop::num::u64::ANY) {
            // For large n, this will variously run for an extremely long time,
            // overflow the stack, or panic due to integer overflow.
            assert!(fib(n) >= n);
        }
    }

    // This is just here so that main can call it
    pub fn do_test_fib() {
        test_fib();
    }
}

fn main() {
    #[cfg(feature = "timeout")]
    fib::do_test_fib();
}