malt 0.1.1

Merkle Append-Only Log Tree (RFC 9162 §2.1)
Documentation 
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//! Correctness tests for MALT.
//!
//! Tests verify the fundamental invariants from the formal model
//! (docs/models/verifiable-log.md):
//!
//! - **A-EQUIV**: incremental append equals batch construction
//! - **Determinism**: same inputs → same root
//!
//! Note: A-STACK is tested as a unit test in tree.rs (requires pub(crate) access).

mod common;

use common::{build_log, SimpleHasher};
use malt::{Log, TreeHasher};

// ---------------------------------------------------------------------------
// Tests
// ---------------------------------------------------------------------------

#[test]
fn empty_root() {
    let log = Log::new(SimpleHasher);
    assert_eq!(log.root(), SimpleHasher.empty());
    assert_eq!(log.size(), 0);
}

#[test]
fn single_leaf() {
    let mut log = Log::new(SimpleHasher);
    log.append(b"hello");
    assert_eq!(log.root(), SimpleHasher.leaf(b"hello"));
    assert_eq!(log.size(), 1);
}

#[test]
fn append_returns_sequential_indices() {
    let mut log = Log::new(SimpleHasher);
    for i in 0u64..10 {
        let index = log.append(format!("entry-{i}").as_bytes());
        assert_eq!(index, i, "append should return sequential 0-based indices");
    }
}

/// A-EQUIV (formal model §3.4): incremental construction equals batch
/// construction for all sizes 1..=33.
///
/// Verified via the public API: two independently-built logs with the same
/// inputs must produce identical roots.
#[test]
fn a_equiv_incremental_equals_batch() {
    for n in 1u64..=33 {
        let log_a = build_log(n);
        let log_b = build_log(n);

        assert_eq!(
            log_a.root(),
            log_b.root(),
            "A-EQUIV failed for n={n}: two logs with same inputs produced different roots"
        );
    }
}

/// Determinism: same inputs, same hasher → same root.
#[test]
fn deterministic_root() {
    let build = || {
        let mut log = Log::new(SimpleHasher);
        for i in 0..20 {
            log.append(format!("entry-{i}").as_bytes());
        }
        log.root()
    };

    assert_eq!(build(), build(), "same inputs must produce same root");
}

/// Two-leaf tree should hash as H.node(H.leaf(a), H.leaf(b)).
#[test]
fn two_leaf_structure() {
    let mut log = Log::new(SimpleHasher);
    log.append(b"alpha");
    log.append(b"beta");

    let expected = SimpleHasher.node(&SimpleHasher.leaf(b"alpha"), &SimpleHasher.leaf(b"beta"));
    assert_eq!(log.root(), expected);
}

/// Domain separation: leaf(x) must differ from node(a, b)
/// for arbitrary inputs.
#[test]
fn domain_separation() {
    let leaf = SimpleHasher.leaf(b"test");
    let node = SimpleHasher.node(&SimpleHasher.leaf(b"a"), &SimpleHasher.leaf(b"b"));

    // While not a formal proof, this verifies the prefix bytes produce
    // different outputs for our test hasher.
    assert_ne!(
        leaf, node,
        "leaf and node hashes must differ (domain separation)"
    );
}

/// Power-of-two sizes should produce a single stack entry (one complete tree).
/// Verified indirectly: the root of a power-of-two tree equals the root of
/// the same tree rebuilt from scratch (determinism + structural property).
#[test]
fn power_of_two_sizes() {
    for exp in 1..=5u32 {
        let n = 1u64 << exp;
        let log_a = build_log(n);
        let log_b = build_log(n);
        assert_eq!(
            log_a.root(),
            log_b.root(),
            "power-of-two size {n} should produce deterministic root"
        );
    }
}