Log Error: Expected invocation on the mock exactly times, but was 0 times

Issue Description

The unit testing logger method produces errors while mocking logger extension methods using Moq.

Moq.MockException: Expected invocation on the mock exactly 2 times, but was 0 times: m => m.Log(LogLevel.Information, It.IsAny(), It.IsAny(), It.IsAny(), It.IsAny>())

The above error was mostly observed while mocking logger extension methods .NET Core 3.0 and above version.

This error could also exist if migrating .NET Core 2.* code to .NET Core 3.* code

Resolution

The issue found seems to be due to the new generic type support introduced in the recent version of the Moq test framework.

I was able to fix the error using the below code base.

 [Fact]                 
        public void BookService_Get_ValidBookID_Success()
        {
            //Arrange
            var _mockBusiness = new Mock<IBusinessLayer>();
            var _mockLogger = new Mock<ILogger<ValuesController>>();
            int input = 12;
            int expectedloggerInvocationCount = 2;
            string expectedResult = "True";
            _mockBusiness.Setup(x => x.PerformBusiness()).Returns(true);

            //Act

            ValuesController controller = new ValuesController(_mockLogger.Object, _mockBusiness.Object);
            var result = controller.Get(input).Result as ObjectResult;

            //Assert

            Assert.Equal(HttpStatusCode.OK, (HttpStatusCode)result.StatusCode);

            _mockLogger.Verify(x => x.Log(LogLevel.Information,
               It.IsAny<EventId>(),
               It.IsAny<It.IsAnyType>(),
               It.IsAny<Exception>(),
               (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()),
               Times.Exactly(2));
     }

Alternatively,

If you still get any compatibility issues, use the below code to verify method invocation. The below code does the same job as Verify methods.

Assert.Equal(2, _mockLogger.Invocations.Count)

References:

• Unit Test and Mock Logger Methods in .NET Core
• Unit Testing Best Practices -Test-Driven Development
• Unit Testing Vs Intergration Best Practices -Test-Driven Development

Did I miss anything else in these resolution steps?

Did the above steps resolve your issue? Please sound off your comments below!

Happy Coding !!

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