How to unit test a circuit breaker?

Question

I am using an external service for metatagging my pages. I implemented circuit breaker as well as fallback for it and is working perfectly. Now I want to write unit tests for it. Any thoughts?

I am pasting some part of my code for your review:

Unity Registration

.RegisterType<ITaggerRepository>(new InjectionFactory(c => Framework.CrossCutter.ApplyAspectsTo((ITaggerRepository)c.Resolve<CachedTaggerRepository>(), "TaggerRepository").Configure<ISlaAspectConfiguration<ITaggerRepository>>(config => config.Fallback = new TaggerRepositoryFallback())
.Proxy));

Fallback implementation:

public class TaggerRepositoryFallback : ITaggerRepository
{
    /// <summary>
    /// Requests the tags.
    /// </summary>
    /// <param name="request">The request.</param>
    /// <returns>Tagger response</returns>
    public TaggerResponse RequestTags(TaggerRequest request)
    {
        return new TaggerResponse
        {
            Url = request.PageUrl,