Mocking ILogger for Azure Functions

ILogger Mocking with Strict behaviour.md

To mock the behavior of ILogger in Azure Functions with MockBehavior.Strict (using Moq) you can use the following mock setup:

var loggerMock = new Mock<ILogger>(MockBehavior.Strict);
    loggerMock.Setup(
        log => log.Log(
            LogLevel.Error,
            It.IsAny<EventId>(), 
            It.IsAny<It.IsAnyType>(),
            It.IsAny<Exception>(),
            (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()));

In the above example a mock setup is done which expects a call to logger.LogError(...).

ILogger Mock Builder

Use a builder pattern such as below to easily add a mocked ILogger to your unit test:

public class LoggerMockBuilder
{
    private readonly Mock<ILogger> _loggerMock;
    public LoggerMockBuilder()
    {
        _loggerMock = new Mock<ILogger>(MockBehavior.Strict);
    }
    public LoggerMockBuilder WithLogLevel(LogLevel level)
    {
        _loggerMock
            .Setup(
                log => log.Log(
                    level,
                    It.IsAny<EventId>(),
                    It.IsAny<It.IsAnyType>(),
                    It.IsAny<Exception>(),
                    (Func<It.IsAnyType, Exception, string>)It.IsAny<object>()));
        return this;
    }
    public Mock<ILogger> Create()
    {
        return _loggerMock;
    }
}

Then create a mock of the logger using the builder in a unit test:

 var loggerMock = new LoggerMockBuilder()
        .WithLogLevel(LogLevel.Warning)
        .Create();