r.model.AsyncSlice;
  const AsyncSliceGroup = tr.model.AsyncSliceGroup;
  const newAsyncSlice = tr.c.TestUtils.newAsyncSlice;
  const newAsyncSliceEx = tr.c.TestUtils.newAsyncSliceEx;
  const newModel = tr.c.TestUtils.newModel;

  test('asyncSliceGroupBounds_Empty', function() {
    const thread = {};
    const g = new AsyncSliceGroup(thread);
    g.updateBounds();
    assert.isTrue(g.bounds.isEmpty);
  });

  test('asyncSliceGroupBounds_Basic', function() {
    const model = new tr.Model();
    const p1 = 