Verify a method is called or not in Unit Test

Question

I have a unit test I am checking whether a method is called once or not so I attempted this way:-

This is my Mock of ILicenseManagerService and I am passing its object through constructor.

    public Mock<ILicenseManagerService> LicenseManagerService { get { return SetLicenseManagerServiceMock(); } }          private Mock<ILicenseManagerService> SetLicenseManagerServiceMock()         {             var licencemangerservicemock = new Mock<ILicenseManagerService>();             licencemangerservicemock.Setup(m => m.LoadProductLicenses()).Returns(ListOfProductLicense).Verifiable();              return licencemangerservicemock;         }          public static async Task<IEnumerable<IProductLicense>> ListOfProductLicense()         {             var datetimeoffset = new DateTimeOffset(DateTime.Now);              var lst = new List<IProductLicense>             {                 GetProductLicense(true, datetimeoffset, false, "1"),                 GetProductLicense(true, datetimeoffset, false, "2"),                 GetProductLicense(true, datetimeoffset, true, "3")             };              return lst;         } 

I am using this mock object to set _licenseManagerService and calling the LoadProductLicenses() in method under test. like this. licences are coming fine.

    var licenses = (await _licenseManagerService.LoadProductLicenses()).ToList(); 

My attempt for verify the call to this method -

     LicenseManagerService.Verify(m => m.LoadProductLicenses(),Times.Once); 

But when I run my unit test, an exception coming that say method is not invoked at all. Where I am doing wrong ?

EDIT @dacastro I am invoking the same mock here is my unit test.

    [TestMethod]         [TestCategory("InApp-InAppStore")]         public async Task return_products_from_web_when_cache_is_empty()         {             // this class basically for setting up external dependencies             // Like - LicenceManagerService in context, i am using this mock only no new mock.             var inAppMock = new InAppMock ();                                 // object of Class under test- I used static method for passing external                      //services for easy to change              var inAppStore = StaticMethods.GetInAppStore(inAppMock);              // method is called in this method             var result = await inAppStore.LoadProductsFromCacheOrWeb();              // like you can see using the same inAppMock object and same LicenseManagerService             inAppMock.LicenseManagerService.Verify(m => m.LoadProductLicenses(),Times.Once);                                 } 

Answer 1

LicenseManagerService.Verify(m => m.LoadProductLicenses(),Times.Once); 

By calling the LicenseManagerService property, you're creating a new mock object. Naturally, no invocations have ever been performed on this instance.

You should change this property's implementation to return the same instance every time it is called.