bootstrapper.cs

protected override NancyInternalConfiguration InternalConfiguration
{
    get
    {
        return
            NancyInternalConfiguration.WithOverrides(x => x.RenderContextFactory = typeof (TestRenderContextFactory));
    }
}

TestRenderContextFactory.cs

public class TestRenderContextFactory : IRenderContextFactory
{
    private IViewResolver viewResolver;
    private IViewCache viewCache;
    
    public TestRenderContextFactory(IViewResolver viewResolver, IViewCache viewCache)
    {
        this.viewResolver = viewResolver;
        this.viewCache = viewCache;
    }
    
    public IRenderContext GetRenderContext(ViewLocationContext viewLocationContext)
    {
        return new DefaultRenderContext(
                        this.viewResolver,
                        viewLocationContext.Context.Items.ContainsKey("DebugViewCache") ? 
                            viewLocationContext.Context.Items["DebugViewCache"] as IViewCache : 
                            this.viewCache,
                        viewLocationContext);
    }
}