soup/tests/test_multipack_invariants.py

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"""v0.37.0 Part E — packing correctness invariants across the multipack stack.
Mirrors Axolotl's ``test_packed_batch_sampler.py:111-117`` quality bar plus
extra cross-module checks that exercise sampler + 4D mask + Jinja analyzer
together. Each test asserts an invariant that, if broken, would silently
corrupt training (hardest class of bug to surface in production).
Invariants:
1. **No duplicates across packs** — every sample index appears at most once
per epoch.
2. **Full coverage** — every sample index appears at least once per epoch.
3. **Pack-len bound** — no bin's total length exceeds
``batch_size × max_seq_length`` (flat mode) or ``max_seq_length``
(real-batches mode).
4. **Mask-segment coherence** — the 4D mask built from a packed bin has
no allowed cross-segment attention pair.
5. **Determinism on identical seed** — sampler order is reproducible.
6. **Stress** — invariants 13 hold on a 5,000-sample random workload.
"""
from __future__ import annotations
import random
import numpy as np
import pytest
from soup_cli.utils.jinja_analyzer import extract_message_fields
from soup_cli.utils.multipack_sampler import (
MultipackBatchSampler,
ffd_bin_pack,
)
from soup_cli.utils.neat_packing import (
build_4d_attention_mask,
tag_sub_sequences,
)
def _flatten_indices(sampler: MultipackBatchSampler) -> list[int]:
flat: list[int] = []
for batch in sampler:
if batch and isinstance(batch[0], list):
for bin_ in batch:
flat.extend(bin_)
else:
flat.extend(batch)
return flat
# ---- Invariants 1-3: sampler-level ---------------------------------------
@pytest.mark.parametrize("seed", [0, 1, 42, 999])
def test_no_duplicates_across_packs(seed):
rng = random.Random(seed)
lengths = [rng.randint(1, 50) for _ in range(200)]
sampler = MultipackBatchSampler(
lengths, batch_max_len=128, batch_size=4,
real_batches=False, seed=seed,
)
seen: set[int] = set()
for batch in sampler:
for idx in batch:
assert idx not in seen, f"duplicate index {idx} in sampler output"
seen.add(idx)
@pytest.mark.parametrize("seed", [0, 1, 42, 999])
def test_full_coverage(seed):
rng = random.Random(seed)
n = 200
lengths = [rng.randint(1, 50) for _ in range(n)]
sampler = MultipackBatchSampler(
lengths, batch_max_len=128, batch_size=4,
real_batches=False, seed=seed,
)
flat = _flatten_indices(sampler)
assert sorted(flat) == list(range(n))
@pytest.mark.parametrize(
"real_batches,batch_size,batch_max_len",
[(False, 1, 64), (True, 4, 64), (True, 8, 32)],
)
def test_pack_len_bound(real_batches, batch_size, batch_max_len):
rng = random.Random(2026)
lengths = [rng.randint(1, batch_max_len) for _ in range(150)]
sampler = MultipackBatchSampler(
lengths, batch_max_len=batch_max_len, batch_size=batch_size,
real_batches=real_batches, seed=0,
)
if real_batches:
for batch in sampler:
for bin_ in batch:
assert sum(lengths[i] for i in bin_) <= batch_max_len
else:
for bin_ in sampler:
assert sum(lengths[i] for i in bin_) <= batch_max_len
# ---- Invariant 4: sampler + 4D mask coherence ----------------------------
def test_mask_built_from_pack_blocks_cross_doc():
# Build a real packed bin via FFD, derive segment IDs, build 4D mask,
# then verify no allowed cross-segment pair exists in the mask.
lengths = [3, 5, 2, 4, 1, 6]
bins = ffd_bin_pack(lengths, max_len=10)
# Take the first multi-document bin — must have >=2 sub-seqs to test.
target_bin = next((b for b in bins if len(b) >= 2), None)
if target_bin is None:
pytest.fail(
"FFD must pack at least 2 docs into one bin given the test "
f"input lengths={lengths}, max_len=10. Got bins={bins}. "
"If this fires after a packer change, the cross-doc invariant "
"is no longer being exercised."
)
boundaries = [0]
cum = 0
for idx in target_bin:
cum += lengths[idx]
boundaries.append(cum)
seg_ids = tag_sub_sequences(boundaries)
seq_arr = np.array([seg_ids], dtype=np.int32)
mask = build_4d_attention_mask(seq_arr, dtype=np.float32)
plane = mask[0, 0]
# For every position i, every j with seg_ids[i] != seg_ids[j] must be
# blocked (large negative).
for i, seg_i in enumerate(seg_ids):
for j, seg_j in enumerate(seg_ids):
if seg_i != seg_j:
assert plane[i, j] < -1e9, (
f"cross-segment leak at ({i},{j}) "
f"seg_i={seg_i} seg_j={seg_j}"
)
# ---- Invariant 5: determinism --------------------------------------------
def test_determinism_across_processes_simulated():
# Simulate two ranks building the sampler with the same seed → identical
# batch order. Critical for DDP correctness.
lengths = [random.Random(7).randint(1, 40) for _ in range(100)]
s1 = list(MultipackBatchSampler(
lengths, batch_max_len=64, batch_size=2,
real_batches=True, seed=11,
))
s2 = list(MultipackBatchSampler(
lengths, batch_max_len=64, batch_size=2,
real_batches=True, seed=11,
))
assert s1 == s2
# ---- Invariant 6: stress test on 5k samples ------------------------------
def test_stress_5k_samples():
rng = random.Random(31337)
n = 5_000
lengths = [rng.randint(1, 200) for _ in range(n)]
sampler = MultipackBatchSampler(
lengths, batch_max_len=512, batch_size=8,
real_batches=False, seed=0,
)
flat = _flatten_indices(sampler)
# No duplicates, full coverage — both invariants in one pass for speed.
assert len(flat) == n
assert sorted(flat) == list(range(n))
# ---- Cross-module: Jinja analyzer + sampler ------------------------------
def test_jinja_analyzer_finds_train_field_for_per_msg_masking():
# The Axolotl chat-template flavour adds {% if m.train %} so per-message
# training masking works. Confirms the analyzer picks it up — needed by
# the v0.37.0 / v0.36.0 train_on_messages_with_train_field gate.
template = (
"{% for m in messages %}"
"{% if m.train %}<train>{{ m.content }}</train>"
"{% else %}{{ m.content }}"
"{% endif %}"
"{% endfor %}"
)
fields = extract_message_fields(template)
assert "train" in fields
assert "content" in fields