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xUnit1039 Error

The type argument to theory data is not compatible with the type of the corresponding test method parameter

Cause

The type argument given to TheoryData or TheoryDataRow is not compatible with the matching parameter in the test method.

Reason for rule

When the data types aren’t compatible, then the test will fail at runtime with a type mismatch, instead of running the test.

How to fix violations

To fix a violation of this rule, make the types in the parameter and theory data compatible.

Examples

Violates

Using TheoryData<> (for v2 and v3)

using Xunit;

public class xUnit1039
{
    public static TheoryData<int> PropertyData =>
        new() { 1, 2, 3 };

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

Using TheoryDataRow<> (for v3 only)

using System.Collections.Generic;
using Xunit;

public class xUnit1039
{
    public static IEnumerable<TheoryDataRow<int>> PropertyData =>
        [new(1), new(2), new(3)];

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

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

public class ClassRowData : IEnumerable<TheoryDataRow<int>>
{
    public IEnumerator<TheoryDataRow<int>> GetEnumerator()
    {
        yield return new(1);
        yield return new(2);
        yield return new(3);
    }

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

public class xUnit1039
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(string _) { }
}

Does not violate

Using TheoryData<> (for v2 and v3)

using Xunit;

public class xUnit1039
{
    public static TheoryData<int> PropertyData =>
        new() { 1, 2, 3 };

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

using Xunit;

public class xUnit1039
{
    public static TheoryData<string> PropertyData =>
        new() { "1", "2", "3" };

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

Using TheoryDataRow<> (for v3 only)

using System.Collections.Generic;
using Xunit;

public class xUnit1039
{
    public static IEnumerable<TheoryDataRow<int>> PropertyData =>
        [new(1), new(2), new(3)];

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

using System.Collections.Generic;
using Xunit;

public class xUnit1039
{
    public static IEnumerable<TheoryDataRow<string>> PropertyData =>
        [new("1"), new("2"), new("3")];

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

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

public class ClassRowData : IEnumerable<TheoryDataRow<int>>
{
    public IEnumerator<TheoryDataRow<int>> GetEnumerator()
    {
        yield return new(1);
        yield return new(2);
        yield return new(3);
    }

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

public class xUnit1039
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _) { }
}

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

public class ClassRowData : IEnumerable<TheoryDataRow<string>>
{
    public IEnumerator<TheoryDataRow<string>> GetEnumerator()
    {
        yield return new("1");
        yield return new("2");
        yield return new("3");
    }

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

public class xUnit1039
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(string _) { }
}
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