Xunit 2.3.0 Unable to pass dates as inline params

Here is a good way to pass strongly typed test data in to xUnit Tests

Blog Post

Source Code

public class SampleData
{
    public int A { get; set; }
    public int B { get; set; }
    public int C => A + B;
}

public class UnitTest1
{
    /// <summary>
    /// The test data must have this return type and should be static
    /// </summary>
    public static IEnumerable<object[]> TestData
    {
        get
        {
            //Load the sample data from some source like JSON or CSV here.
            var sampleDataList = new List<SampleData>
            {
                new SampleData { A = 1, B = 2 },
                new SampleData { A = 3, B = 2 },
                new SampleData { A = 2, B = 2 },
                new SampleData { A = 3, B = 23 },
                new SampleData { A = 43, B = 2 },
                new SampleData { A = 3, B = 22 },
                new SampleData { A = 8, B = 2 },
                new SampleData { A = 7, B = 25 },
                new SampleData { A = 6, B = 27 },
                new SampleData { A = 5, B = 2 }
         };

            var retVal = new List<object[]>();
            foreach(var sampleData in sampleDataList)
            {
                //Add the strongly typed data to an array of objects with one element. This is what xUnit expects.
                retVal.Add(new object[] { sampleData });
            }
            return retVal;
        }
    }

/* Alternate form

    public static IEnumerable<object[]> TestData() 
    {
        yield return new [] { new SampleData { A = 1, B = 2 } };
        yield return new [] { new SampleData { A = 3, B = 2 } };
        yield return new [] { new SampleData { A = 2, B = 2 } };
        yield return new [] { new SampleData { A = 3, B = 23 } };
        yield return new [] { new SampleData { A = 43, B = 2 } };
        yield return new [] { new SampleData { A = 3, B = 22 } };
        yield return new [] { new SampleData { A = 8, B = 2 } };
        yield return new [] { new SampleData { A = 7, B = 25 } };
        yield return new [] { new SampleData { A = 6, B = 27 } };
        yield return new [] { new SampleData { A = 5, B = 2 } };
    }
*/

/* Or:

    public static IEnumerable<object[]> TestData() =>
        from x in new[] { 
            new SampleData { A = 1, B = 2 },
            new SampleData { A = 3, B = 2 },
            new SampleData { A = 2, B = 2 },
            new SampleData { A = 3, B = 23 },
            new SampleData { A = 43, B = 2 },
            new SampleData { A = 3, B = 22 },
            new SampleData { A = 8, B = 2 },
            new SampleData { A = 7, B = 25 },
            new SampleData { A = 6, B = 27 },
            new SampleData { A = 5, B = 2 } }
        select new object[] { x};
    */

    /// <summary>
    /// Specify the test data property with an attribute. This method will get executed 
    /// for each SampleData object in the list
    /// </summary>
    [Theory, MemberData(nameof(TestData))]       
    public void Test1(SampleData sampleData)
    {
        Assert.Equal(sampleData.A + sampleData.B, sampleData.C);
    }
}

The better way to do it currently is to use TheoryData so that you can use strongly typed inputs. Creating strongly typed xUnit theory test data with TheoryData

TheoryData<DateTime> MemberData = new TheoryData<DateTime>
{
 DateTime.Now, 
 new DateTime(), 
 DateTime.Max
}

It appears that this bug is fixed in v2.4.0+ (this feature stopped working in at least v2.3.1?)

If unable to upgrade xunit to a version with the fix then perhaps do the equivalent of what xunit is doing implicitly:

https://github.com/xunit/xunit/blob/07457dab8d0bb188e74e476c062a4a9aeca44711/src/xunit.v3.common/Reflection/Reflector.cs#L88-L92

[Theory]
[InlineData("title 1", "testing 1", 1, "Educational", "2017-3-1", "2018-12-31")]
[InlineData("title 2", "testing 2", 2, "Self Employment", "2017-2-1", "2018-2-28")]
public async Task WhenPassingCorrectData_SuccessfullyCreate(
    string title,
    string description,
    int categoryId,
    string category,
    string startDate, // <-- change from `DateTime` to `string`
    string endDate)   // <-- change from `DateTime` to `string`
{
    var expectedStartDate = DateTime.Parse(startDate); // <-- add this
    var expectedEndDate = DateTime.Parse(endDate);     // <-- add this

    //  rest of test ...

}

Otherwise if have more complicated tests then perhaps use MemberDataAttribute as others suggested.

You can make it explicit with MemberDataAttribute :-

public static readonly object[][] CorrectData =
{
    new object[] { "title 1", "testing 1", 1, "Educational", new DateTime(2017,3,1), new DateTime(2018,12,31)},
    new object[] { "title 2", "testing 2", 2, "Self Employment", new DateTime(2017, 2, 1), new DateTime(2018, 2, 28)}
};

[Theory, MemberData(nameof(CorrectData))]
public async Task WhenPassingCorrectData_SuccessfullyCreate(string title, string description, int categoryId, string category, DateTime startDate, DateTime endDate)
{

}

(You can also make the property return IEnumerable<object[]>, which you'd typically do with yield return enumerator syntax, but I believe the above is the most legible syntax C# has to offer for it at present)