Question

I am testing a Variance method(unit) but double issue is occuring.

    public double Variance()
    {
        return Probablity * (1 - Probablity);
    }

    [Test]
    public void Variance_WithSuccessProbablity02_Returns016()
    {
        var bernoulli = new BernoulliDistribution(0.2);

        Assert.AreEqual(bernoulli.Variance(), 0.16);
    }

This test result is returns fail.
Failed: Expected: 0.160000000000003d But was 0.16d

Answer 1

In NUnit, you can either compare floating point values using an explicit tolerance:

Assert.AreEqual( double expected, double actual, double tolerance );

or you can globally set GlobalSettings.DefaultFloatingPointTolerance to a non-zero value (by default it is 0.0).

There is more information on floating point comparison here.

In your specific case, I recommend you to try this:

Assert.AreEqual(bernoulli.Variance(), 0.16, 1.0e-9);