ENH: Add unit tests for DataFrame snapshot and restore functionality

Author: AkiTheMemeGod

pandas/tests/frame/test_versioning.py

@@ -0,0 +1,54 @@
+# pandas/tests/frame/test_versioning.py
+import pandas as pd
+import pytest
+
+
+def test_snapshot_and_restore_returns_dataframe():
+    df = pd.DataFrame({"x": [1, 2, 3]})
+    sid = df.snapshot("t1")
+    assert sid in df.list_snapshots()
+    df.loc[0, "x"] = 99
+    restored = df.restore(sid)
+    assert list(restored["x"]) == [1, 2, 3]
+
+
+def test_restore_inplace_mutates_dataframe():
+    df = pd.DataFrame({"x": [1, 2, 3]})
+    sid = df.snapshot("t2")
+    df.loc[1, "x"] = 999
+    df.restore(sid, inplace=True)
+    assert list(df["x"]) == [1, 2, 3]
+
+
+def test_drop_and_clear_behaviour():
+    df = pd.DataFrame({"a": [1, 2]})
+    sid1 = df.snapshot("s1")
+    sid2 = df.snapshot("s2")
+    assert set(df.list_snapshots()) == {sid1, sid2}
+    df.drop_snapshot(sid1)
+    assert sid1 not in df.list_snapshots()
+    df.clear_snapshots()
+    assert df.list_snapshots() == []
+
+
+def test_snapshot_on_empty_dataframe():
+    df = pd.DataFrame()
+    sid = df.snapshot()
+    df.loc[0, "a"] = 1
+    restored = df.restore(sid)
+    assert restored.empty
+
+
+def test_copy_does_not_inherit_snapshots():
+    df = pd.DataFrame({"a": [1, 2, 3]})
+    sid = df.snapshot("orig")
+    df2 = df.copy()
+    # design decision: copies do not copy snapshots
+    assert df2.list_snapshots() == []
+    assert sid in df.list_snapshots()
+
+
+def test_missing_snapshot_raises():
+    df = pd.DataFrame({"x": [1]})
+    with pytest.raises(KeyError):
+        df.restore("no-such-snapshot")