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xUnit3001   v2 v3   Error

Classes that are marked as serializable (or created by the test framework at runtime) must have a public parameterless constructor

Cause

Classes which are created by the test framework at runtime, including classes which are serialized, must have a public parameterless constructor.

This includes class which implement:

It also includes classes tagged with [Xunit.Sdk.JsonTypeID] (v3).

Reason for rule

Some classes are created using reflection by the test framework at runtime, and require a parameterless constructor.

When those types are serialized, the body of the constructor should be empty, since all values will come to the object via the deserialization method (IXunitSerializable.Deserialize or IJsonDeserializable.FromJson).

How to fix violations

Add a public parameterless constructor. If the type is serialized, make the constructor empty-bodied, and mark it with [System.Obsolete] so users don’t call it directly.

You may keep any other public constructors with parameters.

Examples

Violates

v2 Core Framework

using Xunit.Abstractions;

public class xUnit3001 : IXunitSerializable
{
    public xUnit3001(int _) { }

    public void Deserialize(IXunitSerializationInfo info) { }

    public void Serialize(IXunitSerializationInfo info) { }
}

v3 Core Framework

[JsonTypeID("json-type")]
public class xUnit3001 : IJsonSerializable, IJsonDeserializable
{
    public xUnit3001(int _) { }

    public void FromJson(IReadOnlyDictionary<string, object?> root) { }

    public string? ToJson() => "{}";
}

using System;
using System.Threading.Tasks;
using Xunit.Runner.Common;
using Xunit.Sdk;

public class xUnit3001 : IRunnerReporter
{
    public xUnit3001(int _) { }

    public bool CanBeEnvironmentallyEnabled => false;

    public string Description => string.Empty;

    public bool ForceNoLogo => false;

    public bool IsEnvironmentallyEnabled => false;

    public string? RunnerSwitch => "custom";

    public ValueTask<IRunnerReporterMessageHandler> CreateMessageHandler(
        IRunnerLogger logger,
        IMessageSink? diagnosticMessageSink) =>
            throw new NotImplementedException();
}

using Xunit.Sdk;

public class xUnit3001 : IXunitSerializable
{
    public xUnit3001(int _) { }

    public void Deserialize(IXunitSerializationInfo info) { }

    public void Serialize(IXunitSerializationInfo info) { }
}

using System;
using Xunit.Sdk;

public class xUnit3001 : IXunitSerializer
{
    public xUnit3001(int _) { }

    public object Deserialize(Type type, string serializedValue) => new();

    public bool IsSerializable(Type type, object? value) => true;

    public string Serialize(object value) => string.Empty;
}

Does not violate

v2 Core Framework

using System;
using Xunit.Abstractions;

public class xUnit3001 : IXunitSerializable
{
    [Obsolete("Called by the de-serializer; should only be called by deriving classes for de-serialization purposes")]
    public xUnit3001() { }

    public xUnit3001(int _) { }

    public void Deserialize(IXunitSerializationInfo info) { }

    public void Serialize(IXunitSerializationInfo info) { }
}

v3 Core Framework

[JsonTypeID("json-type")]
public class xUnit3001 : IJsonSerializable, IJsonDeserializable
{
    [Obsolete("Called by the de-serializer; should only be called by deriving classes for de-serialization purposes")]
    public xUnit3001() { }

    public xUnit3001(int _) { }

    public void FromJson(IReadOnlyDictionary<string, object?> root) { }

    public string? ToJson() => "{}";
}

using System;
using System.Threading.Tasks;
using Xunit.Runner.Common;
using Xunit.Sdk;

public class xUnit3001 : IRunnerReporter
{
    public xUnit3001() { }

    public xUnit3001(int _) { }

    public bool CanBeEnvironmentallyEnabled => false;

    public string Description => string.Empty;

    public bool ForceNoLogo => false;

    public bool IsEnvironmentallyEnabled => false;

    public string? RunnerSwitch => "custom";

    public ValueTask<IRunnerReporterMessageHandler> CreateMessageHandler(
        IRunnerLogger logger,
        IMessageSink? diagnosticMessageSink) =>
            throw new NotImplementedException();
}

using System;
using Xunit.Sdk;

public class xUnit3001 : IXunitSerializable
{
    [Obsolete("Called by the de-serializer; should only be called by deriving classes for de-serialization purposes")]
    public xUnit3001() { }

    public xUnit3001(int _) { }

    public void Deserialize(IXunitSerializationInfo info) { }

    public void Serialize(IXunitSerializationInfo info) { }
}

using System;
using Xunit.Sdk;

public class xUnit3001 : IXunitSerializer
{
    public xUnit3001() { }

    public xUnit3001(int _) { }

    public object Deserialize(Type type, string serializedValue) => new();

    public bool IsSerializable(Type type, object? value) => true;

    public string Serialize(object value) => string.Empty;
}
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