How can I mock the Azure Redis Cache?

Question

How can I mock the Azure Redis Cache?

I would like to write unit test for one of my application which uses Azure Redis Cache. Since I am completely new to mocking and stubbing in writing unit test code, I am looking for help in how I can start with the basic script for mocking/stubbing cache component.

Answer 1

Testing with external resources like databases, files, and caches is integration testing, non unit . What you can test in unit-tests is the fact, that your code is calling caching methods.

So, first, you need an interface of cache service . This interface not only let you test your code, but also let you use different caching servers.

public interface ICache
{
    void Add<T>(string key, TimeSpan lifetime, T value);

    bool TryGet<T>(string key, out T value);

    void Remove(string key);

    . . .
}

Second, you need domain code to test:

public class SleepingMembersService
{
    private readonly TimeStamp _lifetime = TimeStamp.FromMinutes(5);
    private readonly ICache _cache;
    private readonly INotifier _notifier;

    public SleepingMembersService(ICache cache, INotifier notifier)
    {
        _cache = cache;
        _notifier = notifier;
    }

    private string MakeKey(User user) => $"unsleepingUser{user.Id}";

    public void WakeUpIfSleep(IUser user)
    {
        var key = MakeKey(user);
        bool isWaking;
        if (_cache.TryGet(key, out isWaking) && isWaking)
            return;

        notifier.Notify(user.Id, "Wake up!");            
    }

    public void ConfirmImNotSleeping(IUser user)
    {
        var key = MakeKey(user);
        _cache.Add(key, _lifeTime, true);
    }
}

Third, let's make stub cache:

public class StubCache : ICache
{
    public bool TryGetResult { get; set; }

    public bool TryGetValue { get; set; }

    public bool AddValue { get; set; }

    public TimeStamp LifeTimeValue { get; set; }

    void Add<T>(string key, TimeSpan lifetime, T value)
    {
        LifeTimeValue = lifetime;
        AddValue = (bool)(object)value;
    }

    bool TryGet<T>(string key, out T value)
    {
        value = (T)(object)TryGetValue;
        return TryGetResult;
    }

    . . .
}

And finally you can write unit-test:

pubic void ConfirmImNotSleeping_WhenCalled_CallsAdd()
{
    var cache = new StubCache<bool>();
    var notifier = new StubNotifier();
    var service = new SleepingMembersService(cache, notifier);
    var user = new StubUser(1, "John Doe");

    service.ConfirmNotSleeping(user);

    Assert.IsTrue(cache.AddValue);
}

Well, you've checked that the method ConfirmNotSleeping calls the method Add .

Now, you should implement ICache for Redis:

public RedisCache : ICache
{
    private IConnectionMultiplexer connection;

    public bool TryGet<T>(string key, out T value)
    {
        var cache = Connection.GetDatabase();

        var rValue = cache.StringGet(key);
        if (!rValue.HasValue)
        {
            value = default(T);
            return false;
        }

        value = JsonConvert.DeserializeObject<T>(rValue);
        return true;
    }

    . . .    
}

To simplify implement stubs and mocks you can use libraries like Moq . These libraries let you automatically generate stubs and mocks for your purpose. So you test code will look like this:

pubic void ConfirmImNotSleeping_WhenCalled_CallsAdd()
{
    var cacheStub = new Mock<ICache>();
    var notifierStub = new Mock<INotifier>();
    var service = new SleepingMembersService(cache.Object, notifier.Object);
    var userStub = new Mock<IUser>();

    service.ConfirmNotSleeping(user.Object);

    cacheStub.Vertify(x => x.Add(It.IsAny<string>(), It.IsAny<TimeStamp>(), true));
}