Tests: Add undo test for Sculpt trim tool

For Sculpt Undo, certain operators will modify the topology count of the
mesh. These operators are handled separately from normal brush strokes,
and so having tests for an operator that uses this functionality is
beneficial in detecting regressions.

Pull Request: https://projects.blender.org/blender/blender/pulls/139249

tests/python/ui_simulate/test_undo.py

@@ -85,6 +85,14 @@ def _cursor_motion_data_y(window):
     ]
 
 
+def _cursor_motion_data_xy(window):
+    size = _window_size_in_pixels(window)
+    return [
+        (p, p) for p in
+        range(int(size[0] * 0.2), int(size[0] * 0.8), 80)
+    ]
+
+
 def _window_area_get_by_type(window, space_type):
     for area in window.screen.areas:
         if area.type == space_type:
@@ -461,6 +469,44 @@ def view3d_sculpt_dyntopo_and_edit():
     # yield e.ctrl.z()                    # Undo asserts (nested undo call from dyntopo)
 
 
+def view3d_sculpt_trim():
+    """
+    Test that trim functionality can be undone and redone correctly.
+    Operations that work on the entire mesh exercise a different code path from normal sculpt undo.
+    """
+
+    e, t = _test_vars(window := _test_window())
+    yield from _view3d_startup_area_maximized(e)
+    yield from _call_menu(e, "Add -> Mesh -> Torus")
+    yield e.numpad_period()             # View all.
+    yield from _call_by_name(e, "Remove UV Map")
+    yield e.ctrl.tab().s()              # Sculpt via pie menu.
+
+    # Utility to extract current mesh coordinates (used to ensure undo/redo steps are applied properly).
+    def extract_mesh_positions(window):
+        # TODO: Find/add a way to get that info when there is a multires active in Sculpt mode.
+        window.view_layer.update()
+        tmp_mesh = window.view_layer.objects.active.to_mesh(preserve_all_data_layers=True)
+        tmp_cos = [0.0] * len(tmp_mesh.vertices) * 3
+        tmp_mesh.vertices.foreach_get("co", tmp_cos)
+        window.view_layer.objects.active.to_mesh_clear()
+        return tmp_cos
+
+    beginning_positions = extract_mesh_positions(window)
+    yield from _call_by_name(e, "Box Trim")
+    yield from e.leftmouse.cursor_motion(_cursor_motion_data_xy(window))    # Perform the trim
+    after_trim_positions = extract_mesh_positions(window)
+    t.assertNotEqual(beginning_positions, after_trim_positions)
+
+    yield e.ctrl.z()                                                        # Undo Trim
+    after_undo_positions = extract_mesh_positions(window)
+    t.assertEqual(beginning_positions, after_undo_positions)
+
+    yield e.ctrl.shift.z()                                                  # Redo Trim
+    after_redo_positions = extract_mesh_positions(window)
+    t.assertEqual(after_trim_positions, after_redo_positions)
+
+
 def view3d_texture_paint_simple():
     e, t = _test_vars(window := _test_window())
     yield from _view3d_startup_area_maximized(e)