How do I properly test an API Controller that returns json for a non null response?

Question

I have this test method for testing an API controller, that returns a JSON string, for a non null response.

[TestClass]
public class TransactionsTests
{
    [TestMethod]
    public void ColorPerformance_GetChartData_NotNullResponse_Test()
    {
        // Arrange
        string quality = null, cars = null, year = "2015";

        var listColorPerformanceChartData = new List<ColorPerformanceChartData>();
        var mockRepository = new Mock<IColorPerformanceRepository>();
        mockRepository.Setup(x => x.GetChartData(quality, cars, year))
            .Returns(listColorPerformanceChartData);

        var controller = new ColorPerformanceController(mockRepository.Object);

        // Act
        IHttpActionResult actionResult = controller.GetChartData(quality, cars, year);
        var contentResult = actionResult as OkNegotiatedContentResult<object>;

        // Assert
        Assert.IsNotNull(contentResult);
        Assert.IsNotNull(contentResult.Content);
    }
}

This test is passing in that contentResult is not null. However, I am not feeling sure that the test is written properly for the following reasons:

1. contentResult.Content has empty data, in that there is no data being returned from _repository.GetChartData() method, but is not empty because still the json constructed is as follows:

{ categories = {int[0]}, series = { name = "Number of colors", data = {double[0]} } }

2. contentResult.ContentNegotiator, contentResult.Formatter and contentResult.Request all are throwing an exception of InvalidOperationException with the message HttpControllerContext.Configuration must not be null. I don't know why this is happening.

The API Controller:

public class ColorPerformanceController : ApiController
{
    private IColorPerformanceRepository _repository;
    public ColorPerformanceController(IColorPerformanceRepository repository)
    {
        _repository = repository;
    }
    public IHttpActionResult GetChartData(string quality, string cars, string year)
    {
        try 
        {
            var data = ProcessData(quality, cars, year);
            return Ok(data);
        }
        catch (Exception ex)
        {
            return InternalServerError(ex);
        }
    }
    private object ProcessData(string quality, string cars, string year)
    {
        var data = _repository.GetChartData(quality, cars, year);
        return new {
            categories = data.Select(d => d.Id).ToArray(),
            series = new[] { new { name = "Number of colors", data = data.Select(d => d.CumulativePercentage).ToArray() }}
        };
    }
}

IColorPerformanceRepository:

public interface IColorPerformanceRepository
{
    IEnumerable<ColorPerformanceChartData> GetChartData(string quality, string cars, string year);
}

The object returned from the repository implementation:

public class ColorPerformanceChartData
{
    private double _cumulativePercentage;
    public double CumulativePercentage {
        get { return Math.Round(_cumulativePercentage, 2); }
        set { _cumulativePercentage = value; }
    }
    public int Id { get; set; }
}

What am I missing or doing wrong here?

Answer 1

Best practice is you should avoid using anonymous type in this case:

private object ProcessData(string quality, string cars, string year)
    {
        var data = _repository.GetChartData(quality, cars, year);
        return new {
            categories = data.Select(d => d.Id).ToArray(),
            series = new[] { new { name = "Number of colors", data = data.Select(d => d.CumulativePercentage).ToArray() }}
        };
    }

Try defining a class for it so that you can de-serialize the string and check each property:

        // Act
        IHttpActionResult actionResult = controller.GetChartData(quality, cars, year);
        //Notice I use YourClass instead of object here.
        var contentResult = actionResult as OkNegotiatedContentResult<YourClass>;

        // Assert
        Assert.IsNotNull(contentResult);   
        Assert.IsNotNull(contentResult.Content);   
        //Assert all properties of contentResult.Content like categories, series,..

Regarding the exception, try:

var controller = new ColorPerformanceController(mockRepository.Object);
//Add these 2 lines
 controller.Request = new HttpRequestMessage();
 controller.Configuration = new HttpConfiguration();

From http://www.asp.net/web-api/overview/testing-and-debugging/unit-testing-controllers-in-web-api