C# moq how to correctly setup an interface to return a desired value

Question

I've writing various tests for my app and now I got to a problem that I'm unable to solve. The test I'm writing is a simple command that executes and action that modifies a database and then a query to validate that the values are correct. In order to connect to the database my BaseContext gets the connection string from an interface:

        public BaseContext(DbContextOptions options, IConnectionStringProvider connectionStringProvider)
            : base(options)
        {
            _connectionStringProvider   = connectionStringProvider;
        }

        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            if (!optionsBuilder.IsConfigured)
            {
                var connString =_connectionStringProvider.GetConnectionString();
                optionsBuilder.UseOracle(connString);
            }
        }

My connection string provider interface looks like this:

    public interface IConnectionStringProvider
    {
        string GetConnectionString();
        Dictionary<string, string> GetConnectionSession();
    }

And the implementation looks like this:

    public class HttpConnectionStringProvider : IConnectionStringProvider
    {
        public HttpConnectionStringProvider(IConfiguration configuration, IHttpContextAccessor httpContextAccessor)
        {
            _configuration = configuration ?? throw new NullReferenceException(nameof(configuration));
            _httpContext = httpContextAccessor.HttpContext ?? throw new NullReferenceException("HttpContext");
        }

        public string GetConnectionString()
        {
            // Do something with http context and configuration file and return connection string
        }

    }

All this interfaces are registered using autofac.

Then when executing the following test:

        [Test]
        public async Task AddProductTest()
        {

            string connectionString = "fixed_connection_string";

            var mock = new MockRepository(MockBehavior.Default);

            var mockConnectionStringProvider = new Mock<IConnectionStringProvider>();
            mockConnectionStringProvider.Setup(x => x.GetConnectionString())
                .Returns(connectionString);


            await ProductModule.ExecuteCommandAsync(new AddProductCommand(1, "nameProduct"));

            var products = await ProdcutModule.ExecuteQueryAsync(new GetProducts(1));
            // Assert
            Assert.That(products .Status, Is.EqualTo(ResultQueryStatus.Ok));
            Assert.That(products .Value, Is.Not.Empty);
            Assert.That(products .Value.Any(x => x.Name== "nameProduct"));
        }

The IConfiguration and IHttpContextAccessor are mocked using NSubstitute library. But even if I deleted them just to test if IConnectionStringProvider returned the value expected in setup it didn't work.

When running the test in debug I see that steps into the method GetConnectionString() when it should be mocked. I don't know what I'm doing wrong I suppose there is something that I don't understand about testing.

Answer 1

I am curious what you are attempting to do:

Mocking out the connection string for creating someone like a DB connection string or similar, doesn't make a lot of sense. It is part of the base functionality of the DI bits for C# service handling in Setup.

if you want to mess with this, of course you can do it, but the purpose escapes me a bit.

However, if you simply wish to test ProductModule as something you have written, then it makes more sense.

Then when you make this statement:

ProductModule productModule = new ProductModule( - parameters - ); your parameters likely requires a IConnectionStringProvider.

There you need to use your mockConnectionStringProvider.Object

That will allow you to insert your mocked object, as the object used in your ProductModule constructor.