每次测试可以有多个断言吗？

Question

I started looking at FsCheck yesterday, and I am trying to write a simple test, that any instance of DiscountAmount will always have negative value. My question is, is it ok to have multiple asserts within one test. For example, here I am saying that amount from which discountAmount has been created plus discount amount should be 0. But I also say that discount amount should be less than 0. Should this be 2 tests or 1?

    public class DiscountAmountTests
    {
        [Property()]
        public void value_or_created_discountAmount_should_be_negative()
        {
            Arb.Register<AmountArbitrary>();
            Prop.ForAll<Amount>(
                v =>
                {
                    var sut = new DiscountAmount(v);
                    var expectedResult = 0;
                    var result = v + sut;

                    result.Should().Be(expectedResult);

                    sut.Value.Should().BeLessThan(0);

                })
                .QuickCheckThrowOnFailure();
        }

        public class AmountArbitrary
        {
            public static Arbitrary<Amount> Amounts()
            {
                return Arb.Generate<decimal>().Where(x => x > 0)
                    .Select(x => new Amount(x))
                    .ToArbitrary();
            }
        }

    }
}

Answer 1

I would say this is really up to you. I think there are arguments pro and cons - on the one hand, sometimes setup cost is expensive (be it in terms of programmer work to get the system into a particular state, or really compute resource cost, eg you have to do a expensive query to the DB or something) and then in my opinion it's worth making tests more coarsely grained.

The trade-off is that it's typically less clear what the problem is if a coarse grained test fails.

In comparison with unit tests, FsCheck has a bit more setup costs in terms of argument generation, and it is attractive to make FsCheck tests more coarse-grained than unit tests. Also note that FsCheck has some methods like Label , And . Or to combine different properties together while sharing the argument generation, and still allow you to see what part of your test fails, somewhat off-setting one downside.