Object reference not set to an instance of an object in unit test

Question

1.00/5 (1 vote)

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I have a method

C#

public class DeviceInformationGetter
{
    private int _maxRetryTimes;
    private readonly ILogger _logger;

    public DeviceInformationGetter(ILogger logger)
    {
        _logger = logger;
    }

     public int GetMaxRetryTimesFromAppSettings()
    {
        var maxRetryTimes = AsteriskCallFlowService.Configuration.GetSection("appSettings:ServiceMaximumRetryCount").Value;
        return int.Parse(maxRetryTimes);
    }

And the AsteriskCallFlowService.cs is

C#

public class AsteriskCallFlowService : ICallFlowService
{
    private readonly ILogger _logger;
    public static IConfiguration Configuration { get; set; }

Now in unit test, I have

C#

[Fact]
public void Given_AppSettings_Should_Return_Positive_Integer()
{
    var logger = new Mock<ILogger>().Object;
    var deviceInformationGetter = new DeviceInformationGetter(logger);

    var result = deviceInformationGetter.GetMaxRetryTimesFromAppSettings();

    Assert.True(result > 0);

}

But I get the error Object reference not set to an instance of an object

What I have tried:

I know public static IConfiguration Configuration { get; set; } is static and can't have an instance. But I don't want to remove the static. And I don't want DeviceInformationGetter is static as well.

Posted 9-May-16 4:39am

zhshqzyc

Updated 9-May-16 5:28am

v3

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Comments

F-ES Sitecore 9-May-16 10:54am

What line throws the error?

[no name] 9-May-16 10:56am

object not set to an instance of an object

Sergey Alexandrovich Kryukov 9-May-16 10:56am

Please, can you read the question asked for you?
—SA

Sergey Alexandrovich Kryukov 9-May-16 10:56am

In what line?
—SA

[no name] 9-May-16 10:57am

var maxRetryTimes = AsteriskCallFlowService.Configuration.GetSection("appSettings:ServiceMaximumRetryCount").Value;

Sergey Alexandrovich Kryukov 9-May-16 11:00am

Thank you.
Looks correct. Do you have other declarations of AsteriskCallFlowService, so it would give a different meaning to this name? For example, it could also be a member of DeviceInformationGetter. The syntax requires the class AsteriskCallFlowService.
—SA

F-ES Sitecore 9-May-16 11:03am

Now we're all confused, that's not the error you initially said? Use the debugger to see if AsteriskCallFlowService.Configuration.GetSection("appSettings:ServiceMaximumRetryCount") returns anything. You have to remember your unit tests run under the context of the test harness, so if that code normally interacts with the app.config in the proper project, you need the same app.config in the unit test project.

In general you should avoid static methods etc if you plan on unit testing the code as they are usually troublesome to unit test and sometimes impossible without a framework like Microsoft Fakes.

[no name] 9-May-16 11:17am

I have the same configuration file in the unit test project. When I type AsteriskCallFlowService.Configuration in the Immediate Window, it returned null.

F-ES Sitecore 10-May-16 5:47am

That's the root of your problem, you need to work out why it returns null for your unit test but not when the code is running normally.

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OriginalGriff · Answer 1 · 2016-05-09T05:00:00

"object not set to an instance of an object"

C#

var maxRetryTimes = AsteriskCallFlowService.Configuration.GetSection("appSettings:ServiceMaximumRetryCount").Value;

That's a different error to the one you list in the original question.

This is one of the most common problems we get asked, and it's also the one we are least equipped to answer, but you are most equipped to answer yourself.

Let me just explain what the error means: You have tried to use a variable, property, or a method return value but it contains null - which means that there is no instance of a class in the variable.
It's a bit like a pocket: you have a pocket in your shirt, which you use to hold a pen. If you reach into the pocket and find there isn't a pen there, you can't sign your name on a piece of paper - and you will get very funny looks if you try! The empty pocket is giving you a null value (no pen here!) so you can't do anything that you would normally do once you retrieved your pen. Why is it empty? That's the question - it may be that you forgot to pick up your pen when you left the house this morning, or possibly you left the pen in the pocket of yesterdays shirt when you took it off last night.

We can't tell, because we weren't there, and even more importantly, we can't even see your shirt, much less what is in the pocket!

Back to computers, and you have done the same thing, somehow - and we can't see your code, much less run it and find out what contains null when it shouldn't.
But you can - and Visual Studio will help you here. Run your program in the debugger and when it fails, VS will show you the line it found the problem on. You can then start looking at the various parts of it to see what value is null and start looking back through your code to find out why. So put a breakpoint at the beginning of the method containing the error line, and run your program from the start again. This time, VS will stop before the error, and let you examine what is going on by stepping through the code looking at your values.

But we can't do that - we don't have your code, we don't know how to use it if we did have it, we don't have your data. So try it - and see how much information you can find out!