C# – How to Moq Mock a LoggerFactory in C# AspNet Core

cmoqunit testing

I am trying to write some unit tests for controller actions. To do that, I am using XUnit and Moq. The controllers have an ILoggerFactory injected in the constructor. How does one Moq this up for testing?

I have tried mocking a Logger for the controller class, and then mocking up CreateLogger to return the mock Logger, but I keep getting various test runtime NullReferenceExceptions when the LogInformation() function is called.

        //   Logger that yields only disappointment...          
        var mockLogger = new Mock<ILogger<JwtController>>();
        mockLogger.Setup(ml => ml.Log(It.IsAny<LogLevel>(), It.IsAny<EventId>(), It.IsAny<object>(), It.IsAny<Exception>(), It.IsAny<Func<object, Exception, string>>()));
        var mockLoggerFactory = new Mock<ILoggerFactory>();
        mockLoggerFactory.Setup(mlf => mlf.CreateLogger("JwtController")).Returns(mockLogger.Object);

I assume the problem is that LogInformation is being called, and this is an extension method, so how to moq that?

Best Answer

For what it's worth: instead of mocking an ILoggerFactory, you could also pass an instance of NullLoggerFactory. This NullLoggerFactory will return instances of NullLogger. According to the docs, this is a:

Minimalistic logger that does nothing.

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C# – How to cast int to enum

From an int:

YourEnum foo = (YourEnum)yourInt;

From a string:

YourEnum foo = (YourEnum) Enum.Parse(typeof(YourEnum), yourString);

// The foo.ToString().Contains(",") check is necessary for enumerations marked with an [Flags] attribute
if (!Enum.IsDefined(typeof(YourEnum), foo) && !foo.ToString().Contains(","))
{
    throw new InvalidOperationException($"{yourString} is not an underlying value of the YourEnum enumeration.")
}

Update:

From number you can also

YourEnum foo = (YourEnum)Enum.ToObject(typeof(YourEnum) , yourInt);

Java – How to test a class that has private methods, fields or inner classes

Update:

Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.

If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.

Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.

Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);

And for fields:

Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);

Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for getDeclaredField.
2. The setAccessible(true) is required to play around with privates.

Best Answer

Related Solutions

C# – How to cast int to enum

Java – How to test a class that has private methods, fields or inner classes

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