add test for --resume with --collapse-user

Resume with collapsed revision groups was untested: the resume point is
the (articleid, revid) of the last written row, which for collapsed
output is the last revision of a group, and nothing verified that the
replay reconstructs group boundaries and collapsed_revs counts
identically across the resume point. Run sailormoon with
--collapse-user, truncate the output at the midpoint, resume, and
assert the result is identical to an uninterrupted run.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
(cherry picked from commit 6634de51e6)

test/test_resume.py

@@ -806,3 +806,40 @@ def test_resume_revert_detection():
     # Verify revert column matches exactly
     assert_series_equal(df_full["revert"], df_resumed["revert"])
     assert_series_equal(df_full["reverteds"], df_resumed["reverteds"])
+
+
+def test_resume_collapse_user():
+    """Test that --resume with --collapse-user matches an uninterrupted run."""
+    import pandas as pd
+    from pandas.testing import assert_frame_equal
+
+    tester_full = WikiqTester(SAILORMOON, "resume_collapse_full", in_compression="7z", out_format="jsonl")
+
+    try:
+        tester_full.call_wikiq("--collapse-user", "--fandom-2020")
+    except subprocess.CalledProcessError as exc:
+        pytest.fail(exc.stderr.decode("utf8"))
+
+    full_rows = read_jsonl(tester_full.output)
+
+    # Truncate in the middle of a page with several collapsed rows so the
+    # resume point falls between collapsed revision groups
+    middle_idx = len(full_rows) // 2
+
+    tester_partial = WikiqTester(SAILORMOON, "resume_collapse_partial", in_compression="7z", out_format="jsonl")
+    partial_output_path = tester_partial.output
+
+    with open(partial_output_path, 'w') as f:
+        for row in full_rows[:middle_idx + 1]:
+            f.write(json.dumps(row) + "\n")
+
+    try:
+        tester_partial.call_wikiq("--collapse-user", "--fandom-2020", "--resume")
+    except subprocess.CalledProcessError as exc:
+        pytest.fail(exc.stderr.decode("utf8"))
+
+    resumed_rows = read_jsonl(partial_output_path)
+
+    df_full = pd.DataFrame(full_rows)
+    df_resumed = pd.DataFrame(resumed_rows)
+    assert_frame_equal(df_full, df_resumed)