CustomDataAttribute.cs

using Xunit.Sdk;

public class MyTestDataAttribute : DataAttribute
{   
    // Auto-implemented member
    public override IEnumerable<object[]> GetData(MethodInfo testMethod)
    {
        // Create returned object arrays
        yield return new object[]{ someData, someData, someData };
        yield return new object[]{ someData, someData, someData };
    }
}

public class TestClass
{
    [Theory]
    [MyTestDataAttribute]
    public void Test(param one, param two, param three)
    {
        // Test things
    }
}