Mock logger giving me error for ASP.NET Core - asp.net

Question

I was trying to verify whether my log warning message is written via NUnit mocking. I am getting this error message :
An exception of type 'System.NotSupportedException' occurred in Moq.dll but was not handled in user code
Additional information: Invalid verify on a non-virtual (overridable in VB) member: m => m.LogWarning(String.Format("comments not found for part number :{0}", (Object)0), new[] { "111" })
code:
mockLogger.Verify(m => m.LogWarning($"comments not found for part number :{0}", "111"), Times.Exactly(1));
This is happening because NUnit mocking framework does not support extension methods. A few people on stack overflow have suggested to use Log method instead of level wise methods.
What am I missing?

Answer 1

Firstly, you don't need the $ at the start of the string. That's for string interpolation. The LogWarning message is doing a string.format, hence the {0}
Mock frameworks cannot directly mock static methods. The problem in your case is the LogWarning method - that is the static (extension) method.
The simplest way of overcoming this issue is by using a wrapper class. Here's how I got it, in your case.
Firstly I created an interface
public interface IMyLogWarning
{
void LogWarning(string msg, params object[] args);
}
Then I created a class which implements that interface
public class MyLogWarning<T> : IMyLogWarning where T : class
{
private readonly ILogger _logger;
public MyLogWarning(ILogger<T> logger)
{
// Using constructor for DI
_logger = logger;
}
public void LogWarning(string msg, params object[] args)
{
_logger.LogWarning(msg, args);
}
}
The reason for these two is that I'll use these in my code as well as the unit test.
The constructor in the class is setup so it can be populated using dependency injection, something like this in your ConfigureServices method. Feel free to change this; was a quick stab at it on my part.
services.AddTransient<IMyLogWarning, MyLogWarning<MyViewModel>>();
You can then create a unit test that's roughly like this
[Test]
public void LoggingTest_LogAMessage_ConfirmedLogWasRun()
{
// TODO - add the rest of your test code
// Arrange
var warningMsg = "comments not found for part number :{0}";
var partNumber = "111";
var mockLogger = new Mock<IMyLogWarning>();
// Act
mockLogger.Object.LogWarning(warningMsg, partNumber);
// Assert
mockLogger.Verify(m => m.LogWarning(warningMsg, partNumber), Times.Exactly(1));
}