Illustrates zero-friction TDD ideas, use of Sitecore base classes, and tuple deconstructors

CacheFixture.cs

using NSubstitute;
using Sitecore.Abstractions;

namespace UnitTestingDemo
{
  internal static class CacheFixture
  {
    public static (CustomCacheFactory, BaseCacheManager, BaseSettings) CreateCache()
    {
      BaseCacheManager cacheManager = Substitute.For<BaseCacheManager>();
      
      BaseSettings settings = Substitute.For<BaseSettings>();
      return (new CustomCacheFactory(cacheManager, settings), cacheManager, settings);
    }
  }
}

CustomCacheFactory.cs

using Sitecore.Abstractions;
using Sitecore.Caching;

namespace UnitTestingDemo
{
  internal class CustomCacheFactory
  {
    private readonly BaseCacheManager _baseCacheManager;
    private readonly BaseSettings _baseSettings;

    public CustomCacheFactory(BaseCacheManager baseCacheManager, BaseSettings baseSettings)
    {
      _baseCacheManager = baseCacheManager;
      _baseSettings = baseSettings;
    }

    public static string DefaultSize => "10 MB";

    public ICache CreateCache()
    {
      string sizeString = _baseSettings.GetSetting("CustomCacheSize", DefaultSize);
      long size = Sitecore.StringUtil.ParseSizeString(sizeString);
      return _baseCacheManager.GetNamedInstance("OurCustomCache", size, true);
    }
  }
}

MyCacheFactoryShould.cs

using FluentAssertions;
using NSubstitute;
using Sitecore.Abstractions;
using Xunit;

namespace UnitTestingDemo
{
  public class MyCacheFactoryShould
  {
    [Fact]
    public void ReturnAnObject()
    {
      (CustomCacheFactory sut, _ , _) = CacheFixture.CreateCache();

      sut.CreateCache().Should().NotBeNull();
    }

    [Fact]
    public void GetCacheFromSitecore()
    {
      (CustomCacheFactory sut, BaseCacheManager manager, _) = CacheFixture.CreateCache();

      sut.CreateCache();

      manager.Received().GetNamedInstance("OurCustomCache", Arg.Any<long>(), Arg.Any<bool>());
    }

    [Fact]
    public void GetSizeFromSettings()
    {
      (CustomCacheFactory sut, BaseCacheManager manager, BaseSettings settings) = CacheFixture.CreateCache();
      string someSize = "1 MB";
      long expected = Sitecore.StringUtil.ParseSizeString(someSize);
      settings.GetSetting("CustomCacheSize", Arg.Any<string>()).Returns(someSize);

      sut.CreateCache();

      manager.Received().GetNamedInstance(Arg.Any<string>(), expected, Arg.Any<bool>());
    }

    [Fact]
    public void GetDefaultSize()
    {
      (CustomCacheFactory sut, BaseCacheManager manager, BaseSettings settings) = CacheFixture.CreateCache();
      settings.GetSetting( Arg.Any<string>(), CustomCacheFactory.DefaultSize).Returns(CustomCacheFactory.DefaultSize);
      long expected = Sitecore.StringUtil.ParseSizeString(CustomCacheFactory.DefaultSize);

      sut.CreateCache();

      manager.Received().GetNamedInstance(Arg.Any<string>(), expected, Arg.Any<bool>());
    }
  }
}

See https://blog.ploeh.dk/2009/01/28/Zero-FrictionTDD/