iris/tests/cases/plan.rs

//! The tree a seed describes, as a value rather than as widgets.
//!
//! Two things have to hold for a plan to be worth having. Editing a plan has
//! to mean what growing with those edits means, or a scenario reads one thing
//! and the oracle another. And reducing a plan has to end, or a shrinker
//! searching for the smallest counterexample never returns.

use iris::random::{Edits, Kind, Plan, Rng, SpanEdit, plan};
use std::collections::HashMap;

fn some_edits(seed: u64, of: &Plan) -> Edits {
    let mut rng = Rng::new(seed);
    let (mut sized, mut aligned, mut nodes, mut spans) = (0, 0, 0, 0);
    let mut of = of.clone();
    of.walk_mut(&mut |p| {
        if matches!(p.kind, Kind::Span { .. }) {
            spans += 1;
        }
        sized += p.size.is_some() as usize;
        aligned += p.align.is_some() as usize;
        nodes += p.region_node.is_some() as usize;
    });
    let pick =
        |n: usize, rng: &mut Rng| -> Vec<usize> { (0..n).filter(|_| rng.chance()).collect() };
    Edits {
        sizes: pick(sized, &mut rng)
            .into_iter()
            .map(|i| {
                (
                    i,
                    SizeRules {
                        x: SizeRule::Exact(LayoutLen::LEFTOVER),
                        y: SizeRule::Free,
                    },
                )
            })
            .collect(),
        aligns: pick(aligned, &mut rng)
            .into_iter()
            .map(|i| {
                (
                    i,
                    Align {
                        x: Some(AxisAlign::POS),
                        y: None,
                    },
                )
            })
            .collect(),
        nodes: pick(nodes, &mut rng)
            .into_iter()
            .map(|i| (i, true))
            .collect(),
        spans: pick(spans, &mut rng)
            .into_iter()
            .map(|i| {
                (
                    i,
                    SpanEdit {
                        detach: vec![0],
                        attach: 2,
                    },
                )
            })
            .collect::<HashMap<_, _>>(),
        fixed_branches: false,
    }
}

use iris::prelude::*;

/// The two routes to an edited tree are one tree. `plan` resolves edits out
/// of the random stream as it draws; `edited` puts them on a tree that
/// already exists, which is the only route a shrunk plan has, since no seed
/// grows one. A scenario written against either has to read the same.
#[test]
fn editing_a_plan_is_growing_one_with_those_edits() {
    for seed in 1..=60 {
        let bare = plan(seed, 5, &Edits::default());
        let edits = some_edits(seed, &bare);
        assert_eq!(
            bare.edited(&edits),
            plan(seed, 5, &edits),
            "seed {seed}: edited and grown-with-edits disagree"
        );
    }
}

/// No simplification is larger, which is the half of "the shrinker stops" a
/// widget count can see. Most are not smaller either -- a dropped alignment
/// and a simpler leaf both keep the count -- so what rules out circling is
/// that those are one-way too: a `Some` becomes a `None`, and a kind steps
/// down a ladder with no way back up.
#[test]
fn no_simplification_of_a_plan_is_larger_than_it() {
    for seed in 1..=60 {
        let tree = plan(seed, 4, &Edits::default());
        let mut queue = vec![tree];
        let mut seen = 0;
        while let Some(node) = queue.pop() {
            seen += 1;
            if seen > 400 {
                break;
            }
            for small in node.smaller() {
                assert!(
                    small.size() <= node.size(),
                    "seed {seed}: a simplification grew from {} to {}",
                    node.size(),
                    small.size()
                );
                if small.size() < node.size() {
                    queue.push(small);
                }
            }
        }
    }
}

/// Reducing until nothing reduces ends, and ends at something small enough to
/// read rather than at the tree it started from.
#[test]
fn reducing_a_plan_all_the_way_ends() {
    for seed in 1..=30 {
        let mut node = plan(seed, 5, &Edits::default());
        let grown = node.size();
        let mut steps = 0;
        while let Some(next) = node.smaller().into_iter().next() {
            node = next;
            steps += 1;
            assert!(steps < 10_000, "seed {seed}: reducing did not end");
        }
        assert!(
            node.size() < grown.max(2),
            "seed {seed}: reduced {grown} widgets to {}",
            node.size()
        );
    }
}