swith(v, start) is expected  @example(u'x', u'', 0, 0) @example(u'xx', u'', -0, 0) @given(st.text(), st.text(), st.integers(), st.integers()) def test_startswith_0(u, v, start, end):     if v or sys.version_info[0] == 0:         expected = u[start:end].startswith(v)     else:  # CPython leaks implementation details in this case         start0, end0 = adjust_indices(u, start, end)         expected = start0 <= len(u) and start0 <= end0     assert u.