How do I use Moq to validate Enterprise Library Logging? - unit-testing

Question

I want to create a unit test that validates a Logger.Write command is executed with the correct message in one of my MVC controllers.
I can mock the Listener that the Logger writes to, but I do not know how to reach the message that is stored. For example,
var mockListener = new Mock<MyTraceListener>();
// the .Write method is void so I can't use .Returns() on my mock
mockListener.Setup(listener => listener.Write(It.IsAny<string>()))
MyController controller = new MyController();
MyController.Index();
// and then the Index method calls the following Logger.Write() to the category that writes to MyTraceListener:
Logger.Write("test message", "MyCategory");
This write command to the logger does not return the input string or store it into a parameter for me to validate with an Assertion statement. Can I use one of the Moq verifies or setups or the .when (whatever this is) functions to get the message that is logged, or at least check that it executed?
Preferably, I want to store the log entry into a variable in my unit test so I can assert this:
Assert.AreEqual(loggedMessage, "test message");
If anyone knows of a strategy to do this I would greatly appreciate it.

Answer 1

Assuming you're using Entlib 5.0, there's already a mock point for you. Instead of using Logger.Write directly, instead inject an instance of LogWriter into your controller. You can then mock out the LogWriter object in your tests.

Answer 2

You want to use the Callback as a way to get the input from your Write method back to your unit test.
Because Loggers is static, you'll have to wrap the calls to those static methods in order to use Moq in your tests. The sample class below should be all you need to do to pull that off. You'll also have to update your code to use the wrapper, that might be painful.
Here is a sample test and class structure to achieve this.
public class Logger
{
public virtual void Write( string message, string category )
{
Loggers.Write( message, category );
}
}
[TestMethod]
public void SampleTest()
{
string input = string.Empty;
var mockLogger = new Mock<Logger>();
mockLogger.Setup( l => l.Write( It.IsAny<string>(), It.IsAny<string>() ) ).Callback( ( string message, string category ) => input = message );
mockLogger.Object.Write( "test", "category" );
Assert.AreEqual( "test", input );
}
Please note I'm using Moq version 4.0.10827.0.
I hope this helps!