{
  "$type": "site.standard.document",
  "canonicalUrl": "https://johnnyreilly.com/posts/autofac-webapplicationfactory-integration-tests",
  "description": "A bug in ASP.NET Core v3.0 thwarts swapping in Autofac as an IOC container in WebApplicationFactory tests. A workaround exists.",
  "path": "/posts/autofac-webapplicationfactory-integration-tests",
  "publishedAt": "2020-05-21T00:00:00.000Z",
  "site": "at://did:plc:yy3apqjlms24kso7ahn7lbmb/site.standard.publication/3mova7c4nho2b",
  "tags": [
    "asp.net",
    "automated testing"
  ],
  "textContent": "Updated 2nd Oct 2020: _for an approach that works with Autofac 6 and ConfigureTestContainer see this post._\n\n\n\nThis is one of those occasions where I'm not writing up my own work so much as my discovery after in depth googling.\n\nIntegration tests with ASP.NET Core are the best. They spin up an in memory version of your application and let you fire requests at it. They've gone through a number of iterations since ASP.NET Core has been around. You may also be familiar with the TestServer approach of earlier versions. For some time, the advised approach has been using WebApplicationFactory.\n\nWhat makes this approach particularly useful / powerful is that you can swap out dependencies of your running app with fakes / stubs etc. Just like unit tests! But potentially more useful because they run your whole app and hence give you a greater degree of confidence. What does this mean? Well, imagine you changed a piece of middleware in your application; this could potentially break functionality. Unit tests would probably not reveal this. Integration tests would.\n\nThere is a fly in the ointment. A hair in the gazpacho. ASP.NET Core ships with dependency injection in the box. It has its own Inversion of Control container which is perfectly fine. However, many people are accustomed to using other IOC containers such as Autofac.\n\nWhat's the problem? Well, swapping out dependencies registered using ASP.NET Core's IOC requires using a hook called ConfigureTestServices. There's an equivalent hook for swapping out services registered using a custom IOC container: ConfigureTestContainer. Unfortunately, there is a bug in ASP.NET Core as of version 3.0: When using GenericHost, in tests ConfigureTestContainer is not executed\n\nThis means you cannot swap out dependencies that have been registered with Autofac and the like. According to the tremendous David Fowler of the ASP.NET team, this will hopefully be resolved.\n\nIn the meantime, there's a workaround thanks to various commenters on the thread. Instead of using WebApplicationFactory directly, subclass it and create a custom AutofacWebApplicationFactory (the name is not important). This custom class overrides the behavior of ConfigureServices and CreateHost with a CustomServiceProviderFactory:\n\nI'm going to level with you; I don't understand all of this code. I'm not au fait with the inner workings of ASP.NET Core or Autofac but I can tell you what this allows. With this custom WebApplicationFactory in play you get ConfigureTestContainer back in the mix! You get to write code like this:",
  "title": "Autofac, WebApplicationFactory and integration tests"
}