Add a test for reloading (on Python side)

Author: krassowski

tests/test_ynotebook.py

@@ -0,0 +1,96 @@
+from pycrdt import Map
+
+from jupyter_ydoc import YNotebook
+
+
+def make_code_cell(source: str):
+    return {
+        "cell_type": "code",
+        "source": source,
+        "metadata": {},
+        "outputs": [],
+        "execution_count": None,
+    }
+
+
+class AnyInstanceOf:
+    def __init__(self, cls):
+        self.cls = cls
+
+    def __eq__(self, other):
+        return isinstance(other, self.cls)
+
+
+def test_set_preserves_cells_when_unchanged():
+    nb = YNotebook()
+    nb.append_cell(make_code_cell("print('a')\n"))
+    nb.append_cell(make_code_cell("print('b')\n"))
+
+    changes = []
+
+    def record_changes(topic, event):
+        changes.append((topic, event))
+
+    nb.observe(record_changes)
+
+    model = nb.get()
+
+    # Call set with identical structure
+    nb.set(model)
+
+    # No changes should be observed at all
+    assert changes == []
+
+
+def test_set_preserves_cells_with_insert_and_remove():
+    nb = YNotebook()
+    nb.append_cell(make_code_cell("print('a')\n"))  # original 0
+    nb.append_cell(make_code_cell("print('b')\n"))  # original 1 (will remove)
+    nb.append_cell(make_code_cell("print('c')\n"))  # original 2
+
+    # Capture textual content for sanity check
+    cell0_source_text = str(nb.ycells[0]["source"])
+    cell2_source_text = str(nb.ycells[2]["source"])
+
+    # Get the model as Python object
+    model = nb.get()
+
+    # Remove the middle cell and insert a new one between the retained cells
+    cells = model["cells"]
+    assert len(cells) == 3
+
+    # The cell ids are needed for retention logic; keep first and last
+    first = cells[0]
+    last = cells[2]
+
+    # New inserted cell
+    inserted = make_code_cell("print('x')\n")
+    model["cells"] = [first, inserted, last]
+
+    changes = []
+
+    def record_changes(topic, event):
+        changes.append((topic, event))
+
+    nb.observe(record_changes)
+    nb.set(model)
+
+    assert nb.cell_number == 3
+
+    # Content of the first and last cells should remain the same
+    assert str(nb.ycells[0]["source"]) == cell0_source_text
+    assert str(nb.ycells[2]["source"]) == cell2_source_text
+
+    # The middle cell should have a different source now
+    assert str(nb.ycells[1]["source"]) == "print('x')\n"
+
+    # We should have one cell event
+    cell_events = [e for t, e in changes if t == "cells"]
+    assert len(cell_events) == 1
+    event_transactions = cell_events[0]
+    assert len(event_transactions) == 1
+    assert event_transactions[0].delta == [
+        {"retain": 1},
+        {"delete": 1},
+        {"insert": [AnyInstanceOf(Map)]},
+    ]