How to use the ipysheet.current function in ipysheet

def test_current_sheet():
    sheet1 = ipysheet.sheet()
    assert sheet1 is ipysheet.current()
    sheet2 = ipysheet.sheet()
    assert sheet2 is ipysheet.current()
    assert sheet1 is ipysheet.sheet(sheet1)
    assert sheet1 is ipysheet.current()

    sheet3 = ipysheet.sheet('key3')
    assert sheet3 is ipysheet.current()
    sheet4 = ipysheet.sheet('key4')
    assert sheet4 is ipysheet.current()
    assert sheet3 is ipysheet.sheet('key3')
    assert sheet3 is ipysheet.current()
    assert sheet4 is ipysheet.sheet('key4')
    assert sheet4 is ipysheet.current()