Is.InRange Constraint Ambiguity?

[Pierce Louderback]

Hello all,

I wanted to inquire about some behavior in NUnit that confused me at first. I think I now understand why it's doing it, but it seems like it could be worded differently. For reference, I am using NUnit 2.6.3 from NuGet.

I recently started using Constraints with Assert.That, and in this particular case I was trying to verify that something was in range, e.g.:

Assert.That(5.5f, Is.InRange<float>(5.4f, 5.6f));

Which obviously passes, because 5.5 is between 5.4 and 5.6. What doesn't work, however, is when I try to swap the values in Is.InRange, e.g.:

Assert.That(5.5f, Is.InRange<float>(5.6f, 5.4f));

I now get a test failure:
Expected in range (5.6, 5.4)
Actual 5.5f

I've come to the understanding that Is.InRange is checking between a low and a high, but the ambiguity for me lies in the fact that the Intellisense for Is.InRange just says "from" and "to", and then the test result says "expected in range val1, val2". I was confused because reading the test report says that it is not in range (even though the number itself is) and it took me a moment to figure out that it was failing because of the order of arguments. I ended up encountering this when I had a test involving negative numbers - at first I thought it was having difficulty with it being negative, so I tried with positive (as above) and got the same results.

So, in short, I wanted to ask if Is.InRange is intended to be used as min to max (thus forcing direction), despite that intellisense and the test report suggest direction independence.

In the meantime, I am using Assert.AreEqual with a delta, as this particular test is performing a verification that it be within 1% of a tolerance (but was failing with Is.InRange when test cases used negative numbers to create the tolerance values).

Thank you.

[Charlie Poole]

Hi Pierce,

Yes, as you figured out, the two values are really a min and a max. The reason is simply that your use case is not something I ever thought of when I wrote it! If you would like to file a bug at http://github.com/nunit/nunit-framework, it will be easy enough to fix it so your case works.

As an aside, I think that use of Assert.That(myValue, Is.EqualTo(5.4).Within(1).PerCent) is the best way to do a case like this. It's exactly the situation it was designed for. Is.InRange is needed in more general cases, but typical + or - tolerances work better with Within. The "classic" AreEqual, of course, only allows you to specify a fixed value, so you have to calculate it yourself if what you want is a percentage. Additionally, the Assert.That form says exactly what it is you are doing.

Charlie

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[Pierce Louderback]

Excellent, I completely missed the .Within modifier for Is.EqualTo. I actually only recently started using the Constraint model (found it in the documentation and I like the way it reads better), so I'm still a little dry on what's available until I actually use them.

Thanks for the response! (And, as an aside, thanks for all the hard work on NUnit; I've been attached to TDD ever since I started using it)

Pierce

[Charlie Poole]

Hi Pierce,

I'm glad that works for you. Thanks for the bug and congratulations on filing the first new nunit bug on GitHub!

Charlie