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xUnit1037 Error

There are fewer theory data type arguments than required by the parameters of the test method

Cause

When you use TheoryData or TheoryDataRow with [MemberData] or [ClassData], the number of generic types must match the number of parameters in the test method. In this case, you have provided too few types.

Reason for rule

You must provide the correct number of arguments to the test method to run the test.

How to fix violations

To fix a violation of this rule, either add more type parameters to match the method signature, or remove parameters from the test method.

Examples

Violates

Using TheoryData<> (for v2 and v3)

using Xunit;

public class xUnit1037
{
    public static TheoryData<int> PropertyData =>
        new() { 1, 2, 3 };

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

Using TheoryDataRow<> (for v3 only)

using Xunit;

public class xUnit1037
{
    public static IEnumerable<TheoryDataRow<int>> PropertyData =>
        [new(1), new(2), new(3)];

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

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 xUnit1037
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _1, string _2) { }
}

Does not violate

Using TheoryData<> (for v2 and v3)

using Xunit;

public class xUnit1037
{
    public static TheoryData<int, string> PropertyData =>
        new() { { 1, "Hello" }, { 2, "World" } };

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

using Xunit;

public class xUnit1037
{
    public static TheoryData<int> PropertyData =>
        new() { 1, 2, 3 };

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

Using TheoryDataRow<> (for v3 only)

using System.Collections.Generic;
using Xunit;

public class xUnit1037
{
    public static IEnumerable<TheoryDataRow<int, string>> PropertyData =>
        [new(1, "Hello"), new(2, "World")];

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

using Xunit;

public class xUnit1037
{
    public static IEnumerable<TheoryDataRow<int>> PropertyData =>
        [new(1), new(2), new(3)];

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

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

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

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

public class xUnit1037
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _1, string _2) { }
}

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 xUnit1037
{
    [Theory]
    [ClassData(typeof(ClassRowData))]
    public void TestMethod(int _1) { }
}
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