v2 v3 AOT   Warning

xUnit1040

"The theory argument type is nullable, while the type of the corresponding test method parameter is not"

Cause

The type of argument given to TheoryData<>, TheoryDataRow<>, or tuple is marked as nullable, and the test method argument is marked as non-nullable.

Reason for rule

Passing null data to a test method that isn't expecting it could cause runtime errors or unpredictable test results (either false positives or false negatives).

How to fix violations

To fix a violation of this rule, either make the argument non-nullable, or make the test method parameter nullable.

Examples

Violates

Using TheoryData<> (for v2 and v3)

using Xunit;

public class xUnit1040
{
    public static TheoryData<string?> PropertyData =>
        new() { "Hello", "World", default(string) };

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(string _) { }
}

Using TheoryDataRow<> (for v3 only)

using System.Collections.Generic;
using Xunit;

public class xUnit1040
{
    public static IEnumerable<TheoryDataRow<string?>> PropertyData =>
        [new("Hello"), new("World"), new(null)];

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(string _) { }
}

using System.Collections;
using System.Collections.Generic;
using Xunit;

public class ClassRowData : IEnumerable<TheoryDataRow<string?>>
{
    public IEnumerator<TheoryDataRow<string?>> GetEnumerator()
    {
        yield return new("Hello");
        yield return new("World");
        yield return new(null);
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public class xUnit1040
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(string _) { }
}

Using a tuple (for v3 only)

using System.Collections.Generic;
using Xunit;

public class xUnit1040
{
    public static IEnumerable<(int, string?)> PropertyData =>
        [(1, "Hello"), (2, "World"), (3, null)];

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(int _1, string _2) { }
}

using System.Collections;
using System.Collections.Generic;
using Xunit;

public class ClassRowData : IEnumerable<(int, string?)>
{
    public IEnumerator<(int, string?)> GetEnumerator()
    {
        yield return (1, "Hello");
        yield return (2, "World");
        yield return (3, null);
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public class xUnit1040
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _1, string _2) { }
}

Does not violate

Using TheoryData<> (for v2 and v3)

Fix by changing the argument type:

using Xunit;

public class xUnit1040
{
    public static TheoryData<string> PropertyData =>
        new() { "Hello", "World" };

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(string _) { }
}

Fix by changing the parameter type:

using Xunit;

public class xUnit1040
{
    public static TheoryData<string?> PropertyData =>
        new() { "Hello", "World", default(string) };

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(string? _) { }
}

Using TheoryDataRow<> (for v3 only)

Fix by changing the argument type:

using System.Collections.Generic;
using Xunit;

public class xUnit1040
{
    public static IEnumerable<TheoryDataRow<string>> PropertyData =>
        [new("Hello"), new("World")];

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(string _) { }
}

using System.Collections;
using System.Collections.Generic;
using Xunit;

public class ClassRowData : IEnumerable<TheoryDataRow<string>>
{
    public IEnumerator<TheoryDataRow<string>> GetEnumerator()
    {
        yield return new("Hello");
        yield return new("World");
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public class xUnit1040
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(string _) { }
}

Fix by changing the parameter type:

using System.Collections.Generic;
using Xunit;

public class xUnit1040
{
    public static IEnumerable<TheoryDataRow<string?>> PropertyData =>
        [new("Hello"), new("World"), new(null)];

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(string? _) { }
}

using System.Collections;
using System.Collections.Generic;
using Xunit;

public class ClassRowData : IEnumerable<TheoryDataRow<string?>>
{
    public IEnumerator<TheoryDataRow<string?>> GetEnumerator()
    {
        yield return new("Hello");
        yield return new("World");
        yield return new(null);
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public class xUnit1040
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(string? _) { }
}

Using a tuple (for v3 only)

Fix by changing the argument type:

using System.Collections.Generic;
using Xunit;

public class xUnit1040
{
    public static IEnumerable<(int, string)> PropertyData =>
        [(1, "Hello"), (2, "World")];

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(int _1, string _2) { }
}

using System.Collections;
using System.Collections.Generic;
using Xunit;

public class ClassRowData : IEnumerable<(int, string)>
{
    public IEnumerator<(int, string?)> GetEnumerator()
    {
        yield return (1, "Hello");
        yield return (2, "World");
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public class xUnit1040
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _1, string _2) { }
}

Fix by changing the parameter type:

using System.Collections.Generic;
using Xunit;

public class xUnit1040
{
    public static IEnumerable<(int, string?)> PropertyData =>
        [(1, "Hello"), (2, "World"), (3, null)];

    [Theory]
    [MemberData(nameof(PropertyData))]
    public void TestMethod(int _1, string? _2) { }
}

using System.Collections;
using System.Collections.Generic;
using Xunit;

public class ClassRowData : IEnumerable<(int, string?)>
{
    public IEnumerator<(int, string?)> GetEnumerator()
    {
        yield return (1, "Hello");
        yield return (2, "World");
        yield return (3, null);
    }

    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
}

public class xUnit1040
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _1, string? _2) { }
}