Truly Constrained Non-Deterministic Numbers in AutoFixtures

Numbers in AutoFixture are currently created using a strictly monotonically increasing sequence.

var fixture = new Fixture();

var i = fixture.CreateAnonymous<int>();
// Prints -> 1
var l = fixture.CreateAnonymous<long>();
// Prints -> 2
var f = fixture.CreateAnonymous<float>();
// Prints -> 3.0

Starting with version 2.13.0, by applying a specific customization numbers can also be created using a constrained non-deterministic sequence. The new customization is called RandomNumericSequenceCustomization.

var fixture = new Fixture()
    .Customize(new RandomNumericSequenceCustomization());

var i = fixture.CreateAnonymous<int>();
// Prints -> 122
var l = fixture.CreateAnonymous<long>();
// Prints -> 38
var f = fixture.CreateAnonymous<float>();
// Prints -> 147.0

Once the customization has been applied to a Fixture instance subsequent requests for numeric types will yield random non-repeatable numbers in the range of [1, 255]. When requesting more than 255 numbers the range is automatically changed to [256, 32767] and so on.

The default ranges are [1, 255], [256, 32767], and [32768, 2147483647].

Supplying a custom range

To supply a custom range, customize an instance of the Fixture class with an instance of the RandomNumericSequenceGenerator and pass to its constructor a sequence of integer numbers (e.g. -100, 100, 255).

The sequence must be two positive or negative numbers optionally followed by a series of greater numbers.

var fixture = new Fixture();
fixture.Customizations.Add(
    new RandomNumericSequenceGenerator(-100, 100, 255));

var i = fixture.CreateAnonymous<int>();
// Prints -> -95
var l = fixture.CreateAnonymous<long>();
// Prints -> 47
var f = fixture.CreateAnonymous<float>();
// Prints -> -82.0

After applying the customization, numbers are now created in the range of [-100, 100]. However, when requesting more numbers than the range size the range is automatically changed to [101, 255].