def METHOD_NAME(self):
    self.input_variables.append('last_var', size=3)
    self.input_variables.update_indices()
    assert self.input_variables[-1].name == 'last_var', 'Variable not properly appended'
    # test adding an incorrect input
    out_var = OutputVariable('out_var', size=1, index=4)
    try:
        self.input_variables.append(out_var)
    except TypeError:
        pass  # this is what should happen
    else:
        raise TypeError('Error. Able to append an output variable to an input variable')
    self.input_variables.append(InputVariable(name='last_last_var', size=2, index=0))
    assert self.input_variables[-1].name == 'last_last_var', 'Variable not properly appended'