NullReferenceException when mock my handler database

Question

I'm trying to do unit testing to my handler database but I got a nullReferenceException when I call my methods.

This is my handler constructor

public SignalsHandler(IConfiguration configuration, IDbConnection connection)
{
    _dbConnection = connection;
    _settings = configuration.GetSection("SigSettings").Get<SigSettings>();
    if (_settings == null)
        _settings = new SigSettings();
}

And what I do is to Mock that with this on my testing class:

private Mock<IConfigurationSection> _configSectionMock = new Mock<IConfigurationSection>();
private Mock<IConfiguration> _configMock = new Mock<IConfiguration>();
private Mock<IDbConnection> _connection = new Mock<IDbConnection>();
private readonly SignalsHandler _handler;

public SignalsTest()
{
    _configMock.Setup(x => x.GetSection(It.IsAny<string>())).Returns(_configSectionMock.Object);
    _handler = new SignalsHandler(_configMock.Object, _connection.Object);
}

So far so good but when I try to implement some testing it doesn't work. For example, a simple test:

public void CanGetAllSignals()
{
    var result = _handler.GetSignals();
    Assert.IsNotNull(result);
}

I call my .GetSignals() method with my Mock handler. This is the code:

public async Task<List<SignalsDTO>> GetSignals()
{
    var res = new List<SignalsDTO>();
    var sigList = await _dbConnection.QueryAsync<SigSignal>(_settings.Signals);
    foreach (var s in sigList)
        res.Add(new SignalsDTO()
        {
            IDTag = s.IDTag,
            Name = s.Name
        });
    return res;
}

But when I debug my testing method I got:
NullReferenceException:'Object reference not set to an instance of an object.'
at this line:

var sigList = await _dbConnection.QueryAsync<SigSignal>(_settings.Signals);

I suppose this is an error with my mock configuration at my test constructor but I'm not sure about how can I fix this.

Does this answer your question? [What is a NullReferenceException, and how do I fix it?](https://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it) — SomeBody, Oct 26 '21 at 11:08
`CanGetAllSignals` looks flawed - its not awaiting the `Task` — Daniel A. White, Oct 26 '21 at 13:18
yep, that's true, but it doesn't resolve my nullreferenceexception — Weenhallo, Oct 26 '21 at 13:30

Michał Turczyn · Answer 1 · 2021-10-26T13:33:49.430

2

You forgot to setup a return object of a mock. You should define it like:

var connectionMock = new Mock<IDbConnection>();

conectionMock
    .Setup(x => x.QueryAsync<It.IsAnyType>(
        It.IsAny<string>(), 
        It.IsAny<object>(), 
        It.IsAny<IDbTransaction>(), 
        It.IsAny<int?>(), 
        It.IsAny<CommandType?>()
    ))
    .ReturnsAsync(new List<SignalsDTO>());

NOTE: it is not clear what types you use and where, so please adjust that, but the idea is here.

edited Oct 26 '21 at 13:33

answered Oct 26 '21 at 11:16

Michał Turczyn

32,028
14
47
69

What do you mean about my types are not clear? I started to code unit test yesterday so I'm pretty new with this stuff. I can see my error is about I have the connectionString as null and thats why it cannot access my data but your code gives me an error on the It.IsAny() because it expect a String – Weenhallo Oct 26 '21 at 12:42
@Weenhallo please see update. Also, in ReturnsAsync specify sample object that should be returned by the method. – Michał Turczyn Oct 26 '21 at 12:44
Now it gives me another errors(CS0854). It says that an expression tree may not contain a call or invocation that uses optional arguments. My code now is this: conectionMock.Setup(x => x.QueryAsync(It.IsAny())).ReturnsAsync(new List()); – Weenhallo Oct 26 '21 at 13:11
@Weenhallo could you share the signature of method `QueryAsync` ? – Michał Turczyn Oct 26 '21 at 13:15
Task> QueryAsync(this IDbConnection cnn, string sql, object param = null, IDbTransaction transaction = null, int? commandTimeout = null, CommandType? commandType = null); – Weenhallo Oct 26 '21 at 13:27
@Weenhallo see update – Michał Turczyn Oct 26 '21 at 13:34
I got another exception now. System.NotSupportedException: 'Unsupported expression: x => x.QueryAsync(It.IsAny(), It.IsAny – Weenhallo Oct 26 '21 at 13:55
1

@Weenhallo that what i was afraid of. Extension methods cannot be mocked. You need to follow this: https://stackoverflow.com/questions/2295960/mocking-extension-methods-with-moq – Michał Turczyn Oct 26 '21 at 13:58
Finally I fixed it without mocks and giving my configuration another database for testing purposes. Thank you for your time and help – Weenhallo Oct 27 '21 at 07:24

NullReferenceException when mock my handler database

1 Answers1