xUnit3002 v2 v3 Warning

Classes which are JSON serializable should not be tested for their concrete type

Cause

A violation of this rule occurs when a developer is dependent on the concrete type of a JSON serializable object (usually a message sink message implementation).

Reason for rule

Types which are JSON serializable are encouraged to use interfaces to represent them, because they are typically backed by different concrete types depending on whether they exist on the execution side or the runner side.

The message sink messages in the v3 Core Framework follow this pattern: there are concrete versions that live in xunit.v3.core (in the Xunit.v3 namespace) that support serialization only, and versions that live in xunit.v3.runner.common (in the Xunit.Runner.Common namespace) that support both serialization and deserialization. They implement a common interface that lives in xunit.v3.common (in the Xunit.Sdk namespace) that should be used instead.

For example, you should reference IDiscoveryComplete rather than either DiscoveryComplete implementation in all cases other than creating new instances of the message.

How to fix violations

To fix a violation of this rule, reference the class by its primary interface instead of its concrete type.

Examples

Violates

using System;
using Xunit.Sdk;
using Xunit.v3;

public class Xunit3002 : IMessageSink
{
    public bool OnMessage(IMessageSinkMessage message)
    {
        if (message is DiscoveryComplete)
            Console.WriteLine("Discovery is finished!");

        return true;
    }
}

Does not violate

using System;
using Xunit.Sdk;

public class Xunit3002 : IMessageSink
{
    public bool OnMessage(IMessageSinkMessage message)
    {
        if (message is IDiscoveryComplete)
            Console.WriteLine("Discovery is finished!");

        return true;
    }
}