Tests: Add UI test for common mask operations in sculpt mode

This test exercises a common pair of mask operations in sculpt mode, a
dense mesh is created, the sculpt expand operator is used to mask a
region starting from the center, and then this region is inverted.

Pull Request: https://projects.blender.org/blender/blender/pulls/151875

tests/python/CMakeLists.txt

@@ -1492,6 +1492,7 @@ if(WITH_UI_TESTS)
   # list explicitly so changes bisecting/updated are sure to re-run CMake.
   set(_ui_tests
     test_sculpt.asset_shelf_brush_selection
+    test_sculpt.mask_expand_and_invert
     test_tools.sculpt_mode_toolbar
     test_undo.compositor_make_group
     test_undo.text_editor_edit_mode_mix

tests/python/ui_simulate/test_sculpt.py

@@ -86,3 +86,81 @@ def asset_shelf_brush_selection():
     import bpy
     current_brush = bpy.context.tool_settings.sculpt.brush
     t.assertEqual(current_brush.name, "Blob")
+
+
+def _view3d_startup_area_maximized(e):
+    """
+    Set the 3D viewport and set the area full-screen so no other regions.
+    """
+    yield e.shift.f5()                  # 3D Viewport.
+    yield e.ctrl.alt.space()            # Full-screen.
+    yield e.a()                         # Select all.
+    yield e.delete().ret()              # Delete all.
+
+
+def _subdivide_mesh(e, times):
+    yield e.tab()                       # Enter Edit mode.
+    for i in range(times):
+        yield e.ctrl.e().d()                # Subdivide.
+    yield e.tab()                       # Leave Edit mode.
+
+
+def _cursor_motion_data_x(e, start_position, pixels):
+    for x in range(pixels // 10):
+        position = (start_position[0] + x * 10, start_position[1])
+        yield e.cursor_position_set(*position, move=True)
+
+
+def _num_fully_masked_vertices():
+    import bpy
+    import numpy as np
+
+    mesh = bpy.context.object.data
+
+    if not mesh.attributes.get('.sculpt_mask'):
+        return 0
+
+    mask_attr = mesh.attributes['.sculpt_mask']
+
+    num_vertices = mesh.attributes.domain_size('POINT')
+
+    mask_data = np.zeros(num_vertices, dtype=np.float32)
+    mask_attr.data.foreach_get('value', mask_data)
+
+    return np.count_nonzero(mask_data == 1.0)
+
+
+def mask_expand_and_invert():
+    e, t = _test_vars(window := _test_window())
+    yield from _view3d_startup_area_maximized(e)
+
+    yield from _call_menu(e, "Add -> Mesh -> Monkey")
+    yield e.numpad_period()                                     # View monkey
+
+    yield from _subdivide_mesh(e, 3)
+
+    yield e.ctrl.tab().s()                                      # Sculpt via pie menu.
+
+    area = _window_area_get_by_type(window, 'VIEW_3D')
+    position = (area.x + area.width // 2, area.y + area.height // 2)
+    yield e.cursor_position_set(*position, move=True)           # Move mouse to center
+
+    yield e.shift.a()                                           # Expand operator
+
+    yield from _cursor_motion_data_x(e, position, 200)
+    e.leftmouse.tap()
+    yield
+
+    initial_masked_verts = _num_fully_masked_vertices()
+    t.assertEqual(initial_masked_verts, 8548)
+
+    yield e.a()                                                 # Mask pie menu
+    yield e.i()                                                 # Invert
+
+    inverted_masked_verts = _num_fully_masked_vertices()
+    t.assertEqual(inverted_masked_verts, 22598)
+
+    import bpy
+    mesh = bpy.context.object.data
+    total_verts = mesh.attributes.domain_size('POINT')
+    t.assertEqual(initial_masked_verts + inverted_masked_verts, total_verts)