test_stress_graph.py
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| 1 | """Stress tests for the commit DAG and merge-base algorithm. |
| 2 | |
| 3 | Exercises: |
| 4 | - Linear chains of 500 commits. |
| 5 | - Wide fan-out / fan-in (octopus merge shapes). |
| 6 | - Criss-cross merge (ambiguous LCA — should still find *some* ancestor). |
| 7 | - Independent histories (no common ancestor → None). |
| 8 | - find_merge_base symmetry: find_merge_base(a, b) == find_merge_base(b, a). |
| 9 | - Missing commit handles gracefully (None parent pointers in corrupt graphs). |
| 10 | - Diamond topology: four-node diamond always finds the root. |
| 11 | - Double diamond: two diamonds chained together. |
| 12 | - Long parallel branches that converge at a single point. |
| 13 | """ |
| 14 | |
| 15 | import datetime |
| 16 | import pathlib |
| 17 | |
| 18 | import pytest |
| 19 | |
| 20 | from muse.core.types import fake_id |
| 21 | from muse.core.paths import muse_dir |
| 22 | from muse.core.merge_engine import find_merge_base |
| 23 | from muse.core.ids import hash_commit as compute_commit_id, hash_snapshot as compute_snapshot_id |
| 24 | from muse.core.commits import ( |
| 25 | CommitRecord, |
| 26 | write_commit, |
| 27 | ) |
| 28 | |
| 29 | |
| 30 | # --------------------------------------------------------------------------- |
| 31 | # Helpers |
| 32 | # --------------------------------------------------------------------------- |
| 33 | |
| 34 | _SNAP_ID: str = compute_snapshot_id({}) |
| 35 | _BASE_TS: datetime.datetime = datetime.datetime(2026, 1, 1, tzinfo=datetime.timezone.utc) |
| 36 | |
| 37 | |
| 38 | def _write( |
| 39 | root: pathlib.Path, |
| 40 | label: str, |
| 41 | parent: str | None = None, |
| 42 | parent2: str | None = None, |
| 43 | ) -> str: |
| 44 | """Write a commit with a real content-addressed ID. Returns the commit_id.""" |
| 45 | parent_ids = [p for p in (parent, parent2) if p is not None] |
| 46 | cid = compute_commit_id( |
| 47 | parent_ids=parent_ids, |
| 48 | snapshot_id=_SNAP_ID, |
| 49 | message=label, |
| 50 | committed_at_iso=_BASE_TS.isoformat(), |
| 51 | ) |
| 52 | write_commit(root, CommitRecord( |
| 53 | commit_id=cid, |
| 54 | branch="main", |
| 55 | snapshot_id=_SNAP_ID, |
| 56 | message=label, |
| 57 | committed_at=_BASE_TS, |
| 58 | parent_commit_id=parent, |
| 59 | parent2_commit_id=parent2, |
| 60 | )) |
| 61 | return cid |
| 62 | |
| 63 | |
| 64 | @pytest.fixture |
| 65 | def repo(tmp_path: pathlib.Path) -> pathlib.Path: |
| 66 | dot_muse = muse_dir(tmp_path) |
| 67 | (dot_muse / "commits").mkdir(parents=True) |
| 68 | (dot_muse / "refs" / "heads").mkdir(parents=True) |
| 69 | return tmp_path |
| 70 | |
| 71 | |
| 72 | # --------------------------------------------------------------------------- |
| 73 | # Linear chain |
| 74 | # --------------------------------------------------------------------------- |
| 75 | |
| 76 | |
| 77 | class TestLinearChain: |
| 78 | def test_chain_of_500_finds_base(self, repo: pathlib.Path) -> None: |
| 79 | """LCA of two commits on a 500-long linear chain is the shared ancestor.""" |
| 80 | prev: str | None = None |
| 81 | ids: list[str] = [] |
| 82 | for i in range(500): |
| 83 | cid = _write(repo, f"c{i:04d}", prev) |
| 84 | ids.append(cid) |
| 85 | prev = cid |
| 86 | |
| 87 | # Branch off at the commit at index 100 |
| 88 | branch_tip_id = _write(repo, "branch-tip", ids[100]) |
| 89 | |
| 90 | base = find_merge_base(repo, ids[499], branch_tip_id) |
| 91 | assert base == ids[100] |
| 92 | |
| 93 | def test_lca_of_adjacent_commits_is_parent(self, repo: pathlib.Path) -> None: |
| 94 | root_id = _write(repo, "root") |
| 95 | child_id = _write(repo, "child", root_id) |
| 96 | assert find_merge_base(repo, root_id, child_id) == root_id |
| 97 | assert find_merge_base(repo, child_id, root_id) == root_id |
| 98 | |
| 99 | def test_long_chain_lca_symmetry(self, repo: pathlib.Path) -> None: |
| 100 | """find_merge_base(a, b) == find_merge_base(b, a) on a long chain.""" |
| 101 | prev: str | None = None |
| 102 | ids: list[str] = [] |
| 103 | for i in range(100): |
| 104 | cid = _write(repo, f"n{i:03d}", prev) |
| 105 | ids.append(cid) |
| 106 | prev = cid |
| 107 | |
| 108 | left_id = _write(repo, "left", ids[50]) |
| 109 | right_id = _write(repo, "right", ids[50]) |
| 110 | |
| 111 | assert find_merge_base(repo, left_id, right_id) == ids[50] |
| 112 | assert find_merge_base(repo, right_id, left_id) == ids[50] |
| 113 | |
| 114 | def test_same_commit_returns_itself(self, repo: pathlib.Path) -> None: |
| 115 | solo_id = _write(repo, "solo") |
| 116 | assert find_merge_base(repo, solo_id, solo_id) == solo_id |
| 117 | |
| 118 | def test_one_is_ancestor_of_other(self, repo: pathlib.Path) -> None: |
| 119 | """When A is a direct ancestor of B, LCA is A.""" |
| 120 | prev: str | None = None |
| 121 | ids: list[str] = [] |
| 122 | for i in range(20): |
| 123 | cid = _write(repo, f"x{i:02d}", prev) |
| 124 | ids.append(cid) |
| 125 | prev = cid |
| 126 | assert find_merge_base(repo, ids[0], ids[19]) == ids[0] |
| 127 | assert find_merge_base(repo, ids[19], ids[0]) == ids[0] |
| 128 | |
| 129 | |
| 130 | # --------------------------------------------------------------------------- |
| 131 | # Diamond topology |
| 132 | # --------------------------------------------------------------------------- |
| 133 | |
| 134 | |
| 135 | class TestDiamondTopology: |
| 136 | def test_simple_diamond(self, repo: pathlib.Path) -> None: |
| 137 | """ |
| 138 | root |
| 139 | / \\ |
| 140 | L R |
| 141 | \\ / |
| 142 | M (merge commit, not relevant here — just find LCA of L and R) |
| 143 | """ |
| 144 | root_id = _write(repo, "root") |
| 145 | l_id = _write(repo, "L", root_id) |
| 146 | r_id = _write(repo, "R", root_id) |
| 147 | assert find_merge_base(repo, l_id, r_id) == root_id |
| 148 | |
| 149 | def test_double_diamond(self, repo: pathlib.Path) -> None: |
| 150 | """ |
| 151 | A |
| 152 | / \\ |
| 153 | B C |
| 154 | \\ / |
| 155 | D |
| 156 | / \\ |
| 157 | E F |
| 158 | \\ / |
| 159 | G |
| 160 | LCA(E, F) should be D. |
| 161 | """ |
| 162 | a_id = _write(repo, "A") |
| 163 | b_id = _write(repo, "B", a_id) |
| 164 | c_id = _write(repo, "C", a_id) |
| 165 | d_id = _write(repo, "D", b_id, c_id) |
| 166 | e_id = _write(repo, "E", d_id) |
| 167 | f_id = _write(repo, "F", d_id) |
| 168 | assert find_merge_base(repo, e_id, f_id) == d_id |
| 169 | |
| 170 | def test_criss_cross_merge(self, repo: pathlib.Path) -> None: |
| 171 | """ |
| 172 | Criss-cross: A and B are each other's ancestor via two different merge paths. |
| 173 | X → L1 → M1(L1,R1) |
| 174 | X → R1 → M2(R1,L1) |
| 175 | LCA of M1 and M2 should be either L1 or R1 (both are valid LCAs). |
| 176 | The algorithm must not return None or crash. |
| 177 | """ |
| 178 | x_id = _write(repo, "X") |
| 179 | l1_id = _write(repo, "L1", x_id) |
| 180 | r1_id = _write(repo, "R1", x_id) |
| 181 | m1_id = _write(repo, "M1", l1_id, r1_id) |
| 182 | m2_id = _write(repo, "M2", r1_id, l1_id) |
| 183 | |
| 184 | base = find_merge_base(repo, m1_id, m2_id) |
| 185 | # Any of X, L1, R1 is a valid common ancestor; None is not acceptable. |
| 186 | assert base is not None |
| 187 | assert base in {x_id, l1_id, r1_id} |
| 188 | |
| 189 | def test_octopus_three_branch_fan_in(self, repo: pathlib.Path) -> None: |
| 190 | """Three branches that all diverged from the same root.""" |
| 191 | root_id = _write(repo, "root") |
| 192 | ba_id = _write(repo, "branch-a", root_id) |
| 193 | bb_id = _write(repo, "branch-b", root_id) |
| 194 | bc_id = _write(repo, "branch-c", root_id) |
| 195 | |
| 196 | assert find_merge_base(repo, ba_id, bb_id) == root_id |
| 197 | assert find_merge_base(repo, ba_id, bc_id) == root_id |
| 198 | assert find_merge_base(repo, bb_id, bc_id) == root_id |
| 199 | |
| 200 | |
| 201 | # --------------------------------------------------------------------------- |
| 202 | # Independent histories |
| 203 | # --------------------------------------------------------------------------- |
| 204 | |
| 205 | |
| 206 | class TestDisjointHistories: |
| 207 | def test_no_common_ancestor_returns_none(self, repo: pathlib.Path) -> None: |
| 208 | island_a_id = _write(repo, "island-a") |
| 209 | island_b_id = _write(repo, "island-b") |
| 210 | assert find_merge_base(repo, island_a_id, island_b_id) is None |
| 211 | |
| 212 | def test_long_independent_chains_return_none(self, repo: pathlib.Path) -> None: |
| 213 | prev_a: str | None = None |
| 214 | prev_b: str | None = None |
| 215 | last_a = last_b = "" |
| 216 | for i in range(20): |
| 217 | last_a = _write(repo, f"a{i:02d}", prev_a) |
| 218 | last_b = _write(repo, f"b{i:02d}", prev_b) |
| 219 | prev_a = last_a |
| 220 | prev_b = last_b |
| 221 | assert find_merge_base(repo, last_a, last_b) is None |
| 222 | |
| 223 | def test_missing_commit_id_graceful(self, repo: pathlib.Path) -> None: |
| 224 | """Asking for an LCA where one commit doesn't exist should return None, not raise.""" |
| 225 | real_id = _write(repo, "real") |
| 226 | result = find_merge_base(repo, real_id, fake_id("ghost-commit-that-does-not-exist")) |
| 227 | # The ghost has no ancestors, so no common ancestor found. |
| 228 | assert result is None |
| 229 | |
| 230 | |
| 231 | # --------------------------------------------------------------------------- |
| 232 | # Ancestor-set correctness |
| 233 | # --------------------------------------------------------------------------- |
| 234 | |
| 235 | |
| 236 | class TestAncestorCorrectness: |
| 237 | def test_merge_commit_has_both_parents_as_ancestors(self, repo: pathlib.Path) -> None: |
| 238 | root_id = _write(repo, "root") |
| 239 | a_id = _write(repo, "A", root_id) |
| 240 | b_id = _write(repo, "B", root_id) |
| 241 | merge_id = _write(repo, "merge", a_id, b_id) |
| 242 | feature_id = _write(repo, "feature", a_id) |
| 243 | |
| 244 | # LCA of feature and merge: feature branched from A, merge contains A. |
| 245 | # So A is the common ancestor. |
| 246 | base = find_merge_base(repo, feature_id, merge_id) |
| 247 | assert base == a_id |
| 248 | |
| 249 | def test_wide_history_with_shared_root(self, repo: pathlib.Path) -> None: |
| 250 | """100 branches diverging from a shared root, pairwise LCA is root.""" |
| 251 | root_id = _write(repo, "root") |
| 252 | branch_ids = [_write(repo, f"br{i:03d}", root_id) for i in range(50)] |
| 253 | |
| 254 | # Check a sampling of pairs |
| 255 | for i in range(0, 50, 10): |
| 256 | for j in range(i + 1, 50, 10): |
| 257 | assert find_merge_base(repo, branch_ids[i], branch_ids[j]) == root_id |
| 258 | |
| 259 | def test_deep_branch_divergence(self, repo: pathlib.Path) -> None: |
| 260 | """Branches diverge at root, each has 50 commits. LCA is root.""" |
| 261 | root_id = _write(repo, "root") |
| 262 | prev_a: str | None = root_id |
| 263 | prev_b: str | None = root_id |
| 264 | last_a = last_b = root_id |
| 265 | for i in range(50): |
| 266 | last_a = _write(repo, f"da{i:02d}", prev_a) |
| 267 | last_b = _write(repo, f"db{i:02d}", prev_b) |
| 268 | prev_a = last_a |
| 269 | prev_b = last_b |
| 270 | |
| 271 | assert find_merge_base(repo, last_a, last_b) == root_id |
| 272 | |
| 273 | def test_multiple_merge_bases_chain(self, repo: pathlib.Path) -> None: |
| 274 | """A → B → C; branch D from B. LCA of C and D is B.""" |
| 275 | a_id = _write(repo, "A") |
| 276 | b_id = _write(repo, "B", a_id) |
| 277 | c_id = _write(repo, "C", b_id) |
| 278 | d_id = _write(repo, "D", b_id) |
| 279 | assert find_merge_base(repo, c_id, d_id) == b_id |
| 280 | assert find_merge_base(repo, d_id, c_id) == b_id |