RhinoMocks Cheat Sheet by GregFinzer

public interface ISalesTaxService
{
	    Dictionary<string, decimal> GetSalesTaxByPostalCode(string country);
}

public class SalesTaxLogic 
{
	    private readonly Dictionary<string, decimal> _salesTaxByPostalCode;

	    public SalesTaxLogic(ISalesTaxService salesTaxService, string country)
	    {
		        _salesTaxByPostalCode = salesTaxService.GetSalesTaxByPostalCode(country);
	    }

	    public decimal CalcSalesTax(string postalCode, decimal orderTotal)
	    {
		        return Math.Round(_salesTaxByPostalCode[postalCode] * orderTotal, 2, MidpointRounding.AwayFromZero);
	    }

}

[TestClass]
public class InvoiceLogicTests
{
	    [TestMethod]
	    public void When_Calculating_Sales_Tax_It_Should_Not_Be_Zero()
	    {
		        //Arrange
		        ISalesTaxService salesTaxServiceMock = MockRepository.GenerateMock<ISalesTaxService>();
		        Dictionary<string, decimal> salesTaxRates = new Dictionary<string, decimal>();
		        salesTaxRates.Add("43229", .0675M);
		        salesTaxServiceMock.Stub(o => o.GetSalesTaxByPostalCode(null)).IgnoreArguments().Return(salesTaxRates).Repeat.Any();

		        SalesTaxLogic salesTaxLogic = new SalesTaxLogic(salesTaxServiceMock, "USA");

		         //Act
		        decimal orderSalesTax = salesTaxLogic.CalcSalesTax("43229", 19.95M);

		        //Assert
		        Console.WriteLine(orderSalesTax);
		        Assert.AreNotEqual(0, orderSalesTax);
		        salesTaxServiceMock.AssertWasCalled(o => o.GetSalesTaxByPostalCode("USA"));
	    }
}