Unit testing float operations in Visual Studio 2008 Pro

Question

I have some C# unit tests that perform some float/double operations and I would like to unit test them. Assert.AreEqual is insufficient because of rounding errors.

Take unit conversion as an example. 10.5 meters to feet has a conversion factor of 3.281 so I get 34.4505. Using a more accurate conversion factor gives me 34.4488189. I want to test this within, say, 0.1 (so 34.3488-34.5488 would pass the test).

I could certain manually test the value with a tolerance in my unit test but that's highly repetitive and the failure message wouldn't be very descriptive (again without having to write my own Assert failure message):

Assert.IsTrue(Math.Abs(34.4488189 - value) < 0.1);

How can I unit test my float operations to within a certain error tolerance? I cannot find any Assert classes that do this that come with VS. Am I missing it or do I have to roll my own?

Are there standard practices in testing floats/doubles to keep in mind?

Answer 1

You could take a look at the NUnit framework:

//Compare Float values
Assert.AreEqual(float expected, float actual,
float tolerance);
Assert.AreEqual(float expected, float actual, 
   float tolerance, string message);

//Compare Double values
Assert.AreEqual(double expected, double actual, 
   double tolerance);
Assert.AreEqual(double expected, double actual,
double tolerance, string message)

(Above taken from this article)

More listed here.

Answer 2

NUnit can compare within a tolerance by providing a third argument of the AreEqual method. Have a look at NUnit Equality Asserts

Visual Studio Unit Testing also has this: AreEqual Method (Double, Double, Double, String)

Answer 3

I'm on my phone so forgive the lack of code/links.

There's a question on here about favourite c# extensions where people have extended built-in type such as string. You could extend the float type with a method that would work like this:

Myfloat.IsInTolerance(34.8f, 0.1f)

..which would return true if the Myfloat float was 0.1 either side of 34.8. It could make it less laborious.

Answer 4

Assert.AreEqual in MSTest has overloads that accept a delta (error tolerance) parameter:

public static void AreEqual (double expected, double actual, double delta)

for example:

Assert.AreEqual(34.4488189, value, 0.1);

or, for the smallest possible tolerance:

Assert.AreEqual(34.4488189, value, double.Epsilon);