proptest 0.6.0

//-
// Copyright 2017 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.

//! Strategies for generating `bool` values.

use strategy::*;
use test_runner::*;

use rand::Rng;

/// The type of the `ANY` constant.
#[derive(Clone, Copy, Debug)]
pub struct Any(());

/// Generates boolean values by picking `true` or `false` uniformly.
///
/// Shrinks `true` to `false`.
pub const ANY: Any = Any(());

impl Strategy for Any {
    type Value = BoolValueTree;

    fn new_value(&self, runner: &mut TestRunner) -> NewTree<Self> {
        Ok(BoolValueTree(runner.rng().gen()))
    }
}

/// Generates boolean values by picking `true` with the given `probability`
/// (1.0 = always true, 0.0 = always false).
///
/// Shrinks `true` to `false`.
pub fn weighted(probability: f64) -> Weighted {
    Weighted(probability)
}

/// The return type from `weighted()`.
#[derive(Clone, Copy, Debug)]
pub struct Weighted(f64);

impl Strategy for Weighted {
    type Value = BoolValueTree;

    fn new_value(&self, runner: &mut TestRunner) -> NewTree<Self> {
        Ok(BoolValueTree(runner.rng().next_f64() < self.0))
    }
}

/// The `ValueTree` to shrink booleans to false.
#[derive(Clone, Copy, Debug)]
pub struct BoolValueTree(bool);

impl ValueTree for BoolValueTree {
    type Value = bool;

    fn current(&self) -> bool { self.0 }
    fn simplify(&mut self) -> bool {
        let r = self.0;
        self.0 = false;
        r
    }
    fn complicate(&mut self) -> bool {
        let r = self.0;
        self.0 = true;
        !r
    }
}

#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn test_sanity() {
        check_strategy_sanity(ANY, None);
    }
}