Documentation of the InRange constraint does not mention whether from...to also allows negative ranges, e.g. from 0 to -10

[maettu-this]

Referring to https://docs.nunit.org/articles/nunit/writing-tests/constraints/RangeConstraint.html, the documentation misses information on whether from...to also allows a negative range, e.g. from 0 to -10. Why can this be important? Sometimes an assertion needs a tolerance, e.g. Is.InRange(data.Length, (data.Length + (int)(Math.Round(data.Length * tolerance)))) where tolerance can be a positive or negative value. From the documentation it is not clear whether this can possibly work, or wether to must be a value larger than from. Only looking at the code (or decompiling) reveals:

if (from.CompareTo(to) > 0)
{
	throw new ArgumentException("from must be less than to");
}

(NUnit 2.6.4.14350)

I personally would prefer that InRange allowed positive and negative ranges. And in any case, documentation thereof should be improved.

[mikkelbu]

@maettu-this The range constraint allows negative ranges, but it does not allow range specified in decreasing order, so you have to phrase it like

Assert.That(someValue, Is.InRange(-10, 0));

I your case I guess you need to add logic to determine where to place data.Length and (data.Length + (int)(Math.Round(data.Length * tolerance))) in the constraint.

I'll just see if we get other comments, but otherwise I think we should improve the documentation. I don't think we should support ranges in decreasing order as that does not make sense from a mathematical view - e.g. [0, -10] is an empty set, so the constraint would always fail. That being said I never used this constraint (or known that it existed), so I don't fell that strongly about it.

[maettu-this]

@mikkelbu I can reason the argueing mathematically seen. However, in my opinion from and to not necessary need to mean min and max. Also consider the implications on the test code:

// The "InRange" constraint requires that "from must be less than to" (https://github.com/nunit/docs/issues/872):
var from = Math.Min(data.Length, (data.Length + (int)(Math.Round(data.Length * tolerance))));
var to   = Math.Max(data.Length, (data.Length + (int)(Math.Round(data.Length * tolerance))));

Assert.That(someValue, Is.InRange(from, to));

Opposed to a simpler:

Assert.That(someValue, Is.InRange(data.Length, (data.Length + (int)(Math.Round(data.Length * tolerance)))));

And also consider that enabling decreasing ranges wouldn't mean a breaking change, as all existing code is so far required to use increasing ranges, thus is not impacted.

[stevenaw]

I also don't feel strongly one way or another about the behavior here, and I'd probably want to experiment a bit at a computer before forming an opinion.

If we did decide to keep the existing behavior, we may want to consider renaming the parameters to min and max to clarify intent.

[maettu-this]

@stevenaw min and max would definitely underline the semantics. lower and upper would be alternatives, i.e. the lower and upper boundaries of the range. I have seen various pieces of software which use these terms with ranges. But still I'd prefer more flexibility with from and to.

[stevenaw]

@maettu-this Sorry, but I'm starting to lean towards @mikkelbu suggestion as well based on a bit of experimentation with other APIs which people may be used to and expect similar behaviour.

It looks as though SQL's BETWEEN clause - or at least the MSSQL flavour of it - requires that value1 be lower than value2. Something like this will always yield an empty resultset:

WHERE BETWEEN 0 AND -10

I've also seen similar behaviour within dotnet itself. Enumerable.Range() takes a start/count instead of from/to but the method is similarly-enough named that I could see expectations for similar behaviour. It looks like it also requires a positive count and does not support decrementing sets. For example, the following will throw an ArgumentOutOfRangeException:

Enumerable.Range(0, -10)

I'll also leave this open for a bit to see if there's any other opinions from team members

[manfred-brands]

My few cents.

Unit tests should be independent, i.e. stateless, so it shouldn't matter if you execute one in order 1, 2, 3 or in 3, 2, 1 or even 2, 1, 3 in parallel.

[maettu-this]

Unit tests should be independent, i.e. stateless, so it shouldn't matter if you execute one in order 1, 2, 3 or in 3, 2, 1 or even 2, 1, 3 in parallel.

@manfred-brands That was never in question. This issue is about a single assertion within a single test case.

[stevenaw]

I've transferred this to the documenation repo since it sounds like we want to keep the behaviour the same as it is today