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//! Unit tests for `Shrinker::node_program`.
use crate::native::bignum::BigInt;
use crate::native::core::choices::IntegerChoice;
use crate::native::core::{ChoiceKind, ChoiceNode, ChoiceValue, Spans};
use crate::native::shrinker::{ShrinkRun, Shrinker};
fn int_node(value: i128) -> ChoiceNode {
ChoiceNode::new(
ChoiceKind::Integer(IntegerChoice {
min_value: BigInt::from(0),
max_value: BigInt::from(100),
shrink_towards: BigInt::from(0),
}),
ChoiceValue::Integer(BigInt::from(value)),
false,
)
}
#[test]
fn node_program_one_deletes_single_node_at_a_time() {
// Accepting predicate: every prefix is interesting, so deletion at
// every position should succeed.
let initial = vec![int_node(1), int_node(2), int_node(3), int_node(4)];
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => (true, nodes.to_vec(), Spans::new()),
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial,
Spans::new(),
);
shrinker.node_program(1);
// All nodes deletable → result is empty.
assert!(shrinker.current_nodes.is_empty());
}
#[test]
fn node_program_two_deletes_pairs_adaptively() {
// Accepting predicate; node_program(2) deletes 2 nodes at a time.
// Starting with 6 nodes, the adaptive repeats land at 3 ⇒ all gone.
let initial = vec![
int_node(1),
int_node(2),
int_node(3),
int_node(4),
int_node(5),
int_node(6),
];
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => (true, nodes.to_vec(), Spans::new()),
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial,
Spans::new(),
);
shrinker.node_program(2);
assert!(shrinker.current_nodes.is_empty());
}
#[test]
fn node_program_respects_predicate_rejecting_partial_deletes() {
// Predicate accepts only sequences whose length is a multiple of 2.
// node_program(2) keeps shape parity, so we can delete *any* number
// of pairs. node_program(1) can't apply because each odd-length
// candidate is rejected.
let initial = vec![
int_node(1),
int_node(2),
int_node(3),
int_node(4),
int_node(5),
int_node(6),
];
// Test 1: node_program(1) — each candidate has odd length → rejected.
{
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => (nodes.len() % 2 == 0, nodes.to_vec(), Spans::new()),
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial.clone(),
Spans::new(),
);
shrinker.node_program(1);
assert_eq!(shrinker.current_nodes.len(), 6);
}
// Test 2: node_program(2) — each candidate has even length → accepted.
{
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => (nodes.len() % 2 == 0, nodes.to_vec(), Spans::new()),
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial,
Spans::new(),
);
shrinker.node_program(2);
assert_eq!(shrinker.current_nodes.len(), 0);
}
}
#[test]
fn node_program_no_op_on_empty_or_too_long() {
// Empty initial → nothing to do.
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => (true, nodes.to_vec(), Spans::new()),
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
Vec::new(),
Spans::new(),
);
shrinker.node_program(3);
assert_eq!(shrinker.current_nodes.len(), 0);
// n == 0 should also be a no-op.
let initial = vec![int_node(1)];
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => (true, nodes.to_vec(), Spans::new()),
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial,
Spans::new(),
);
shrinker.node_program(0);
assert_eq!(shrinker.current_nodes.len(), 1);
}
/// Initial counterexample is a run-length-encoded sequence
/// (1) (2, 2) (3, 3, 3) (4, 4, 4, 4) (5, 5, 5, 5, 5) where each "block"
/// starts with the count n and is followed by n more copies of n.
/// Predicate: a block reaching n==4 is the interesting one; the
/// trailing (5,...) block should be shrinkable away by `node_program`
/// deletion at lengths 1..=4.
#[test]
fn node_program_deletes_short_ranges() {
let mut initial: Vec<ChoiceNode> = Vec::new();
for i in 1..=5_i128 {
for _ in 0..=i as usize {
initial.push(int_node(i));
}
}
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => {
// Walk run-length-encoded blocks. A block consists of
// a leading integer `n` followed by `n` more copies of
// `n`. Interesting iff a block has n == 4 and all
// values in the block validate.
let mut idx = 0;
let mut interesting = false;
while idx < nodes.len() {
let n = match &nodes[idx].value {
ChoiceValue::Integer(v) => i128::try_from(v).unwrap(),
_ => return (false, nodes.to_vec(), Spans::new()),
};
let block_end = idx + 1 + n.max(0) as usize;
if block_end > nodes.len() {
// Truncated block: not interesting and not invalid;
// just bail.
break;
}
for k in idx + 1..block_end {
match &nodes[k].value {
ChoiceValue::Integer(v) if i128::try_from(v).unwrap() == n => {}
_ => return (false, nodes.to_vec(), Spans::new()),
}
}
if n == 4 {
interesting = true;
}
idx = block_end;
}
(interesting, nodes.to_vec(), Spans::new())
}
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial,
Spans::new(),
);
for k in 1..=4 {
shrinker.node_program(k);
}
// The minimum is the single 4-block: 5 nodes total ([4, 4, 4, 4, 4]).
// The shrinker may converge faster or slower than that, but the
// overall length should drop substantially from 20.
assert!(
shrinker.current_nodes.len() < initial_node_count(),
"node_program failed to shrink: still {} nodes",
shrinker.current_nodes.len()
);
}
fn initial_node_count() -> usize {
// 1+2+3+4+5+5 = 20 (since the loop's inclusive end produces n+1
// copies of n for n >= 1).
20
}
/// Start from 1000 false booleans followed by a true: the predicate
/// accepts iff the sequence eventually reaches a true. `node_program("X")`
/// (delete-one with adaptive `find_integer` repeats) should collapse
/// to a single `true` within a tight call budget.
#[test]
fn node_program_adaptively_deletes_long_false_run() {
use crate::native::core::choices::BooleanChoice;
let mut initial: Vec<ChoiceNode> = (0..1000)
.map(|_| {
ChoiceNode::new(
ChoiceKind::Boolean(BooleanChoice),
ChoiceValue::Boolean(false),
false,
)
})
.collect();
initial.push(ChoiceNode::new(
ChoiceKind::Boolean(BooleanChoice),
ChoiceValue::Boolean(true),
false,
));
let mut shrinker = Shrinker::with_probe(
Box::new(|run| match run {
ShrinkRun::Full(nodes) => {
// Predicate: at least one true present. The realised
// sequence stops at the first true (draw-until-true
// semantics).
let mut realised: Vec<ChoiceNode> = Vec::new();
let mut interesting = false;
for n in nodes {
realised.push(n.clone());
if matches!(n.value, ChoiceValue::Boolean(true)) {
interesting = true;
break;
}
}
(interesting, realised, Spans::new())
}
ShrinkRun::Probe { .. } => (false, Vec::new(), Spans::new()),
}),
initial,
Spans::new(),
);
shrinker.node_program(1);
// The shrink target collapses to a single [true].
assert_eq!(shrinker.current_nodes.len(), 1);
}