How to use the deal.pre function in deal

def test_init(self):
        with self.subTest(text='init has not raised any exceptions'):
            func = deal.pre(lambda x: x > 0)

        with self.subTest(text='validator'):
            func = deal.pre(lambda x: x > 0)(lambda x: x)
            with pytest.raises(deal.PreContractError):
                func(-2)

        with self.subTest(text='message'):
            func = deal.pre(lambda x: x > 0, message='TEST')(lambda x: x)
            try:
                func(-2)
            except AssertionError as e:
                self.assertEqual(e.args[0], 'TEST')

        with self.subTest(text='exception'):
            func = deal.pre(lambda x: x > 0, exception=NameError)(lambda x: x)
            with pytest.raises(NameError):
                func(-2)

        with self.subTest(text='exception with name'):
            func = deal.pre(lambda x: x > 0, exception=NameError('TEST'))(lambda x: x)
            with self.subTest(text='exception/exception'):
                with pytest.raises(NameError):
                    func(-2)
            with self.subTest(text='exception/message'):

    @deal.pre(scheme, message='old message')
    def func(name):
        return name * 2

        @deal.pre(lambda name: name != 'Oleg')
        def func(name):
            return name * 2

    @deal.pre(lambda x: x > 0 or 'new message', message='old message')
    def double(x):
        return x * 2

@deal.pre(lambda a, b: a > 0)
@deal.pre(lambda a, b: b > 0, message='b must be positive')
def div(a: int, b: int) -> float:
    assert isinstance(a, int)
    assert isinstance(b, int)
    assert a > 0
    assert b > 0
    return a / b

def test_main(self):
        func = deal.pre(lambda x: x > 0)(lambda x: x)

        with self.subTest(text='good'):
            self.assertEqual(func(4), 4)

        with self.subTest(text='error'):
            with pytest.raises(deal.PreContractError):
                func(-2)

def test_contract_returns_message():
    func = deal.pre(lambda x: x > 0 or 'TEST')(lambda x: x)
    assert func(4) == 4

    with pytest.raises(deal.PreContractError):
        func(-2)

    try:
        func(-2)
    except deal.PreContractError as e:
        assert e.args[0] == 'TEST'

def test_correct_exceptions_raised_on_contract_fail():
    func = deal.pre(lambda x: x > 0)(lambda x: x)
    with pytest.raises(deal.PreContractError):
        func(-2)

    func = deal.pre(lambda x: x > 0, message='TEST')(lambda x: x)
    try:
        func(-2)
    except AssertionError as e:
        assert e.args[0] == 'TEST'

    func = deal.pre(lambda x: x > 0, exception=NameError)(lambda x: x)
    with pytest.raises(NameError):
        func(-2)

    func = deal.pre(lambda x: x > 0, exception=NameError('TEST'))(lambda x: x)
    with pytest.raises(NameError):
        func(-2)
    try:
        func(-2)
    except NameError as e:
        assert e.args[0] == 'TEST'

def test_debug(self):
        func = deal.pre(lambda x: x > 0, debug=True)(lambda x: x * 2)
        deal.switch(debug=False)
        with self.subTest(text='good'):
            func(-2)
        deal.switch(debug=True)
        with self.subTest(text='error'):
            with pytest.raises(deal.PreContractError):
                func(-2)

            @deal.pre(lambda self, x: x > 0)
            def method2(self, y):
                return self.y