How do I verify a method was called exactly once w

Question

How do I verify a method was called exactly once with Moq? The Verify() vs. Verifable() thing is really confusing.

Answer 1

You can use Times.Once(), or Times.Exactly(1):

mockContext.Verify(x => x.SaveChanges(), Times.Once());
mockContext.Verify(x => x.SaveChanges(), Times.Exactly(1));

Here are the methods on the Times class:

• AtLeast - Specifies that a mocked method should be invoked times times as minimum.
• AtLeastOnce - Specifies that a mocked method should be invoked one time as minimum.
• AtMost - Specifies that a mocked method should be invoked times time as maximum.
• AtMostOnce - Specifies that a mocked method should be invoked one time as maximum.
• Between - Specifies that a mocked method should be invoked between from and to times.
• Exactly - Specifies that a mocked method should be invoked exactly times times.
• Never - Specifies that a mocked method should not be invoked.
• Once - Specifies that a mocked method should be invoked exactly one time.

Just remember that they are method calls; I kept getting tripped up, thinking they were properties and forgetting the parentheses.

Answer 2

Imagine we have are building a calculator with one method for adding 2 integers. Let's further imagine the requirement is that when the add method is called, it calls the print method once. Here is how we would test this:

public interface IPrinter
{
    void Print(int answer);
}

public class ConsolePrinter : IPrinter
{
    public void Print(int answer)
    {
        Console.WriteLine("The answer is {0}.", answer);
    }
}

public class Calculator
{
    private IPrinter printer;
    public Calculator(IPrinter printer)
    {
        this.printer = printer;
    }

    public void Add(int num1, int num2)
    {
        printer.Print(num1 + num2);
    }
}

And here is the actual test with comments within the code for further clarification:

[TestClass]
public class CalculatorTests
{
    [TestMethod]
    public void WhenAddIsCalled__ItShouldCallPrint()
    {
        /* Arrange */
        var iPrinterMock = new Mock<IPrinter>();

        // Let's mock the method so when it is called, we handle it
        iPrinterMock.Setup(x => x.Print(It.IsAny<int>()));

        // Create the calculator and pass the mocked printer to it
        var calculator = new Calculator(iPrinterMock.Object);

        /* Act */
        calculator.Add(1, 1);

        /* Assert */
        // Let's make sure that the calculator's Add method called printer.Print. Here we are making sure it is called once but this is optional
        iPrinterMock.Verify(x => x.Print(It.IsAny<int>()), Times.Once);

        // Or we can be more specific and ensure that Print was called with the correct parameter.
        iPrinterMock.Verify(x => x.Print(3), Times.Once);
    }
}

Answer 3

Test controller may be :

  public HttpResponseMessage DeleteCars(HttpRequestMessage request, int id)
    {
        Car item = _service.Get(id);
        if (item == null)
        {
            return request.CreateResponse(HttpStatusCode.NotFound);
        }

        _service.Remove(id);
        return request.CreateResponse(HttpStatusCode.OK);
    }

And When DeleteCars method called with valid id, then we can verify that, Service remove method called exactly once by this test :

 [TestMethod]
    public void Delete_WhenInvokedWithValidId_ShouldBeCalledRevomeOnce()
    {
        //arange
        const int carid = 10;
        var car = new Car() { Id = carid, Year = 2001, Model = "TTT", Make = "CAR 1", Price=2000 };
        mockCarService.Setup(x => x.Get(It.IsAny<int>())).Returns(car);

        var httpRequestMessage = new HttpRequestMessage();
        httpRequestMessage.Properties[HttpPropertyKeys.HttpConfigurationKey] = new HttpConfiguration();

        //act
        var result = carController.DeleteCar(httpRequestMessage, vechileId);

        //assert
        mockCarService.Verify(x => x.Remove(carid), Times.Exactly(1));
    }