.scrollTop = start_offset.top;
    scroller.scrollLeft = start_offset.left;

    child.scrollIntoView({block: alignment, inline: alignment});

    assert_equals(scroller.scrollTop, expected_offset.top,
        `${alignment} sets top`);
    assert_equals(scroller.scrollLeft, expected_offset.left,
        `${alignment} sets left`);
  }

  test(function() {
    // child, being positioned at (0, 0) and having size 400 x 400 covers the
    // scrollport at scroll offsets (0,0) and (100, 100).
    test_alignment(