[Feature request] Natural number sequence Theory

[xp44mm]

Natural number sequence Theory is the simplest form of testing our theory with data.

Currently, I use the InlineDataAttribute attribute to represent array indices

type NaturalNumberSeqTest(output: ITestOutputHelper) =
    [<Theory>]
    [<InlineData(0)>]
    [<InlineData(1)>]
    [<InlineData(2)>]
    [<InlineData(3)>]
    member _.``Natural number sequence``(i:int) =
        let expect = [0;1;2;3]
        let actual = [0;1;2;3]
        Should.equal expect.[i] actual.[i]

Feature request: same code using NaturalAttribute attribute

    [<Theory>]
    [<Natural(4)>]
    member _.``Natural number sequence``(i:int) =
        let expect = [0;1;2;3]
        let actual = [0;1;2;3]
        Should.equal expect.[i] actual.[i]

[bartelink]

TheoryData is a good general base for stuff like this, rather than having such specific helpers. Recent releases if V2 have a constructor that takes an IEnumerable<T>, which woks well with F# Seq expressions and/or other list comprehensions.

Something like this:

type NaturalNumberSeqTest(output: ITestOutputHelper) =

    let nats = TheoryData(seq { 0..4 })
    [<Theory; MemberData(nameof nats)>]
    let ``Natural number sequence``(i:int) =
        let expect = [0;1;2;3]
        let actual = [0;1;2;3]
        Should.equal expect.[i] actual.[i]

(The fact that your example is a bit contrived gives away the fact that this is not your true requirement, but my general contention that having lots of generation helpers like this becomes very messy remains)

[bradwilson]

@bartelink's answer is a reasonable solution here.

Additionally, for re-usability you can create your own data sources by creating an attribute that derives from DataAttribute. Sample (utilizing TheoryData) in C#:

public sealed class NaturalAttribute : DataAttribute
{
	private readonly TheoryData<int> values;

	public NaturalAttribute(int count) :
		this(0, count)
	{ }

	public NaturalAttribute(int start, int count) =>
		values = new TheoryData<int>(Enumerable.Range(start, count));

	public override IEnumerable<object[]> GetData(MethodInfo testMethod) =>
		values;
}

[xp44mm]

Your code has been worked perfectly for me, thank you. @bradwilson