Can Autofixture.Create return a negative value?

Question

Actually, the following method always returns a positive integer:

var fixture = new Fixture();
var someInt = fixture.Create<int>();

Is it possible that one day, the feature evolves and begins to return a negative integer? Or is there an official reason it actually returns an always positive integer
If not, is there some documentation hidden somewhere telling it?

To keep on using autofixture, I'd like to know if some changes are foreseen.

score 16 · Accepted Answer · answered Jul 14 '15 at 13:27

The author of Autofixture discusses this on his blog. This post specifies that the current implementation will always return positive numbers since they are deemed "safer" in general, so I don't think this will change in the near future.

The whole point of AutoFixture is to generate anonymous test data. You are asking for an integer which can be a negative number. To be 100% safe, I wouldn't rely on the implicit assumption that all future implementations only return positive numbers. You can make this more explicit by providing a custom SpecimenBuilder:

fixture.Customizations.Add(new PositiveIntegerBuilder());

More information about custom specimen builders can be found here.

Thanks for the idea of the custom specimen builder. – Deblaton Jean-Philippe Jul 14 '15 at 13:33 — Deblaton Jean-Philippe, Jul 14 '15 at 13:33

score 15 · Answer 2 · edited May 23 '17 at 12:18

15

As user prgmtc points out, one option is through a custom ISpecimenBuilder.

Another option is to supply a custom range, by using the built-in RandomNumericSequenceGenerator class, as shown below:

[Fact]
public void FixtureCreatesNegativeNumbers()
{
    var fixture = new Fixture();
    fixture.Customizations.Add(
        new RandomNumericSequenceGenerator(-900, -100));

    var i = fixture.Create<int>();
    // Prints -> -711
    var l = fixture.Create<long>();
    // Prints -> 618
    var f = fixture.Create<float>();
    // Prints -> -78.0
}

edited May 23 '17 at 12:18

Community

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answered Jul 14 '15 at 15:07

Nikos Baxevanis

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Or how about just `var i = -fixture.Create()`? – Neo Sep 26 '18 at 14:57
That could possibly work only when using the default generator for numbers which yields positive integers. I'd prefer the [explicit (is better than implicit)](https://www.python.org/dev/peps/pep-0020/) approach. – Nikos Baxevanis Sep 28 '18 at 03:47
Indeed, and the coder would know if that's the case. Nothing to do with being explicit or implicit. And nothing to do with Python. ;) – Neo Sep 28 '18 at 11:25
@Neo this only works if you always need a negative number. If you want a bit of both then it won't do. – jeromej Sep 15 '22 at 13:29
@jeromej That was literally my point, and the point of the question. – Neo Sep 15 '22 at 23:15

DeSass · Answer 3 · 2020-09-16T12:51:58.950

var i = fixture.Create<uint>();

Only if the original code being tested expected a uint type parameter.

Wouldvar i = Math.Abs(fixture.Create<int>()) work for you

To answer the original question

int by defintion can be negative.
fixture.Create, by definition should not return negative int.

I would assume that the authors of AutoFixture will not change something that crucial so lightly. I would use fixture.Create<int>

score -3 · Answer 4 · answered Jul 14 '15 at 13:15

-3

In so far as the datatype is capable of supporting negative numbers, yes. Who knows what madness the developers might foist upon us - but it is unlikely they would want to do that.

In summary, possible? Yes. Likely? No.

answered Jul 14 '15 at 13:15

Martin Milan

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Your answer is very obvious and useless to me. I reformulated the question. – Deblaton Jean-Philippe Jul 14 '15 at 13:26

Can Autofixture.Create return a negative value?

4 Answers4