Using Moq with a template method

Question

I am trying to Moq a Rabbit MQ method.

ValueTask BasicPublishAsync<TProperties>(string exchange, string routingKey,
    bool mandatory, TProperties basicProperties, ReadOnlyMemory<byte> body,
    CancellationToken cancellationToken = default)
    where TProperties : IReadOnlyBasicProperties, IAmqpHeader;

What is the correct form of:

mockRabbitModel.Setup(a => a.BasicPublishAsync<It.IsSubtype<IAmqpHeader>>(
    It.IsAny<string>() /*exchange*/,
    It.IsAny<string>() /*routingKey*/,
    It.IsAny<bool>() /* mandatory*/,
    // ??????,
    It.Is<ReadOnlyMemory<byte>>(b =>
        this.TestSentMessage(b, (expected, actual) => 
            Assert.AreEqual(expected, actual.Command))),
    It.IsAny<CancellationToken>()));

Moq can't work with TProperties directly and I have seen various ideas for mapping the argument with ??????

Answer 1

As you have used It.IsSubtype<IAmqpHeader> as the generic parameter for the BasicPublishAsync, you should use the same type for the basicProperties wrapped into a It.IsAny.

Here is a simplified version of your code:

public interface IFoo
{
    ValueTask BasicPublishAsync<TProperties>(string key1, TProperties properties);
}

Then the mocking should be done like this:

var foo_mock = new Mock<IFoo>();
foo_mock.Setup(foo => foo.BasicPublishAsync<It.IsSubtype<int>>(It.IsAny<string>(), It.IsAny<It.IsSubtype<int>>()))
        .Returns(() => ValueTask.FromException(new Exception("BlahBlah")));

Here you can find a working sample code: https://dotnetfiddle.net/zSEE5D

---

UPDATE #1

To tackle the multi interface constraint you can introduce a custom TypeMatcher:

The interfaces:

public interface IFoo
{
    ValueTask BasicPublishAsync<TProperties>(string key1, TProperties properties) where TProperties: IA, IB;
}


public interface IA {}
public interface IB {}
internal interface IAB: IA, IB {} // just for testing

The type matcher

[TypeMatcher]
public class FooTypeMatcher<T> : IA, IB, ITypeMatcher
    where T : IA, IB
{
    bool ITypeMatcher.Matches(Type typeArgument)
    {
        return typeof(T).IsAssignableFrom(typeArgument);
    }
}

The mock setup:

var foo_mock = new Mock<IFoo>();
foo_mock.Setup(foo => foo.BasicPublishAsync<FooTypeMatcher<IAB>>(It.IsAny<string>(), It.IsAny<FooTypeMatcher<IAB>>()))
        .Returns(() => ValueTask.FromException(new Exception("BlahBlah")));

Here you can find a working sample code: https://dotnetfiddle.net/5kOz8W