Precision error when calculating small volumes

[mortenbock]

Describe the bug
Given this unit test:

[Test]
public void Foo()
{
    Length length = Length.FromMillimeters(10);
    Length width = Length.FromMillimeters(10);
    Length height = Length.FromMillimeters(10);

    Volume volume = length * width * height;

    Assert.That(volume.CubicMillimeters, Is.EqualTo(1000));
}

The test fails with:

Expected: 1000
But was:  1000.0000000000001d

It seems that working with small units means that the precision of the calculations are not correct?

Using version 5.1.0

[angularsen]

Duplicate of #1193, please continue the discussion there.

[angularsen]

Actually, your question is not the exact same issue as 1193 since it does not involve units in the equality, so I will answer here.

This is generally due to double precision in arithmetic, you can't assume it will always be perfectly 1000. When comparing double values, you should always specify a max error tolerance. Most unit test frameworks provide this or you can write your own.

For example, FluentAssertions has value.Should().BeApproximately(3.14, 0.01);