public void Test_S2CellUnion_LeafCellsCovered()
{
S2CellUnion cell_union = new();
Assert.Equal(0UL, cell_union.LeafCellsCovered());
var ids = new List <S2CellId>
{
// One leaf cell on face 0.
S2CellId.FromFace(0).ChildBegin(S2.kMaxCellLevel)
};
cell_union = new S2CellUnion(ids);
Assert.Equal(1UL, cell_union.LeafCellsCovered());
// Face 0 itself (which includes the previous leaf cell).
ids.Add(S2CellId.FromFace(0));
cell_union = new S2CellUnion(ids);
Assert.Equal(1UL << 60, cell_union.LeafCellsCovered());
// Five faces.
cell_union.Expand(0);
Assert.Equal(5UL << 60, cell_union.LeafCellsCovered());
// Whole world.
cell_union.Expand(0);
Assert.Equal(6UL << 60, cell_union.LeafCellsCovered());
// Add some disjoint cells.
ids.Add(S2CellId.FromFace(1).ChildBegin(1));
ids.Add(S2CellId.FromFace(2).ChildBegin(2));
ids.Add(S2CellId.FromFace(2).ChildEnd(2).Prev());
ids.Add(S2CellId.FromFace(3).ChildBegin(14));
ids.Add(S2CellId.FromFace(4).ChildBegin(27));
ids.Add(S2CellId.FromFace(4).ChildEnd(15).Prev());
ids.Add(S2CellId.FromFace(5).ChildBegin(30));
cell_union = new S2CellUnion(ids);
UInt64 expected = 1UL + (1UL << 6) + (1UL << 30) + (1UL << 32) +
(2UL << 56) + (1UL << 58) + (1UL << 60);
Assert.Equal(expected, cell_union.LeafCellsCovered());
}
