How to compare decimals knowing there is room for error

Question

I have two different ways to calculate a value. Once both methods run, I get the following:

decimal a = 145.2344;
decimal b = 145.2345;

I have a unit test:

  Assert.AreEqual(a,b);

I want to be able to account for a +/- .0001 difference. How can I add this rule?

Answer 1

In NUnit's constraint model, you can do this:

Assert.That(Math.Abs(a-b), Is.LessThan(0.0001M));

Better yet, make it a function:

void AssertDiff(decimal a, decimal b, decimal diff = 0.0001) {
     Assert.That(Math.Abs(a-b), Is.LessThan(diff));
}

EDIT : In MS Unit Test Framework, do this:

void AssertDiff(decimal a, decimal b, decimal diff = 0.0001) {
     Assert.IsTrue(Math.Abs(a-b) < diff);
}

Answer 2

Simple:

if (Math.Abs(a-b) < 0.0001m)
    // equal