Organising unit tests into partial classes

When unit testing a service, I tend to have a base class where I do all the setting up/initialisation. For each method in the service, I’d have a separate unit test class which derives from the base class. For example, if I want to unit test two methods GetAllNews and GetNewsById in SampleNewsService, I’ll have a SampleNewsServiceTestsBase where I initialise the service with all its required dependencies. I then have a separate unit test class derived from SampleNewsServiceTestsBase to test all scenarios for each of the method in the SampleNewsService.

using NUnit.Framework;

namespace SampleWebApplicationTests
{
    [TestFixture]
    public class SampleNewsServiceTestsBase
    {
        [SetUp]
        public void SetUp()
        {
            // Service initialisation and other setups
        }
    }
}

Base class – SampleNewsServiceTestsBase.cs

using NUnit.Framework;

namespace SampleWebApplicationTests
{
    [TestFixture]
    public class GetNewsByIdTests : SampleNewsServiceTestsBase
    {
        [Test]
        public void SampleTest()
        {
            // Test logic goes here
        }
    }
}

Tests for GetNewsById method – GetNewsByIdTests.cs

using NUnit.Framework;

namespace SampleWebApplicationTests
{
    [TestFixture]
    public class GetAllNewsTests : SampleNewsServiceTestsBase
    {
        [Test]
        public void SampleTest()
        {
            // Test logic goes here
        }
    }
}

Tests for GetAllNews method – GetAllNewsTests.cs

This way has been working well for me but recently I come across another way to organise unit tests which I think is quite nice. This is by adding unit tests for each method as a partial class to the base class. I would rename the base class to SampleNewsServiceTests as this makes more sense and that there are no more derived classes. The unit tests then look like the following.

using NUnit.Framework;

namespace SampleWebApplicationTests
{
    [TestFixture]
    public partial class SampleNewsServiceTests
    {
        [SetUp]
        public void Setup()
        {
            // Service initialisation and other setups
        }
    }
}

The setup or ‘base’ class – SampleNewsServiceTests.cs

using NUnit.Framework;

namespace SampleWebApplicationTests
{
    [TestFixture]
    public partial class SampleNewsServiceTests
    {
        [Test]
        public void GetNewsByIdSampleTest()
        {
            // Test logic goes here
        }
    }
}

Tests for GetNewsById method – SampleNewsServiceTests.GetNewsById.cs

using NUnit.Framework;

namespace SampleWebApplicationTests
{
    [TestFixture]
    public partial class SampleNewsServiceTests
    {
        [Test]
        public void GetAllNewsSampleTest()
        {
            // Test logic goes here
        }
    }
}

Tests for GetAllNews method – SampleNewsServiceTests.GetAllNews.cs

I would suggest using an extension for Visual Studio like File Nesting to nest all the method test files under the setup file to keep the solution cleaner.

Conclusion

I honestly don’t have a preference between the two ways. These two ways are very similar in a way. It doesn’t matter which way you go with though, just pick one and stick with it. The only thing I think partial class way does better is that you don’t have any derived test classes – composition over inheritance.