The Problem: Validating HttpClient Handlers in ASP.NET Core

When configuring HttpClient using AddHttpClient(), developers often attach important features using message handlers. These handlers form a step-by-step pipeline that processes outgoing requests. Examples include retry logic, request logging, or authentication.

The problem appears when you want to test that the correct handlers are attached. It is common to write integration tests that resolve your service from the DI container, call methods, and inspect behavior. But this does not confirm whether the handler chain is correct.

A handler can silently fail to attach due to a typo, incorrect registration, or a missing service. You may have code like this:

services.AddHttpClient("ClientService")
    .AddHttpMessageHandler<HttpRetryHandler>()
    .AddHttpMessageHandler<HttpLogHandler>();

But you cannot verify from your test that the constructed pipeline includes these handlers. Even worse, Visual Studio can display the handler chain in the debugger, but this ability is not accessible through public APIs.

Without a direct way to look inside the pipeline, teams cannot automatically verify one of the most important parts of their application’s networking stack. The next Snipp explains why this limitation exists.