public void GivenCustomerWhenCustomerIsPresentThenReturnTotalPremium() { // Arrange var mockPremiumCalculator = new Mock <IPremiumCalculator>(); mockPremiumCalculator.Setup(c => c.CalculateTotalPremium(It.IsAny <decimal>())).Returns(52.5M); var mockCustomer = this.GetCustomerMock(); var premiumCalculatorBuilder = new CustomerBuilder(mockPremiumCalculator.Object); premiumCalculatorBuilder.Set(mockCustomer); // Act premiumCalculatorBuilder.CalculateTotalPremium(); // Assert mockPremiumCalculator.Verify(c => c.CalculateTotalPremium(It.IsAny <decimal>()), Times.Once); Assert.AreEqual(52.5M, mockCustomer.TotalPremium); }