Arrange, act, assert

To bring order into our unit tests, there are certain patterns to follow. One of the most common and popular patterns is the triple A (AAA) syntax, where the A's stand for:

• Arrange
• Act
• Assert

The best way to visualize this is in code. Let's see how it works in C# code and then move on to the F# equivalent:

using NUnit.Framework;
using SUT = Company.System.BL.Calculators;

namespace Company.System.Tests.BL.Calculators.PriceCalculator
{
    public class GetPrice
    {
        [Test]
        public void ShouldReturnZeroOnEmptyOrder()
        {
            // Arrange
            var priceCalculator = new SUT.PriceCalculator();
            var order = new { };
            
            // Act
            var result = priceCalculator.GetPrice(order);

            // Assert
            Assert.That(result, Is.EqualTo(0), "Expecting zero price when order is empty");
        }
    }
}

I usually put the comments in there, to communicate to the reader that I'm...