def METHOD_NAME(self) -> None:
    """Test the subst_path() method on nested substitution of strings.
    """
    self.env.Append(L1 = ['a', 'b'],
                    L2 = ['c', 'd'],
                    L3 = ['$L2'])
    pl = SCons.PathList.PathList(['$L1'])
    result = pl.subst_path(self.env, 'y', 'z')
    assert result == ('a', 'b'), result
    self.env.Append(L1 = ['$L2'])
    pl = SCons.PathList.PathList(['$L1'])
    result = pl.subst_path(self.env, 'y', 'z')
    assert result == ('a', 'b', 'c', 'd'), result
    self.env.Append(L1 = ['$L3'])
    pl = SCons.PathList.PathList(['$L1'])
    result = pl.subst_path(self.env, 'y', 'z')
    assert result == ('a', 'b', 'c', 'd', 'c', 'd'), result