I’ve recently been playing around with a tool called Scrutor. I’m using this in a project and it’s working really well; however, I came across an issue (not related to the tool per se). I had created an interface, but hadn’t yet written a class to implement it. Scrutor realised this was the case and started moaning at me. Obviously, I hadn’t written any unit tests around the non-existent class, but I did have a reasonably good test coverage for the rest of the project; however the project wouldn’t actually run.
To be clear, what I’m saying here is that, despite the test suite that I had running successfully, the program wouldn’t even start. This feels like a very askew state of affairs.
Some irrelevant background, I had a very strange issue with my Lenovo laptop, whereby, following a firmware update, the USB-C ports just stopped working - including to accept charge - so my laptop died. Sadly, I hadn’t followed good practice, with commits, and so part of my code was lost.
I’ve previously played around with the concept of integration tests in Asp.Net Core+, so I thought that’s probably what I needed here. There are a few articles and examples out there, but I couldn’t find anything that worked with Asp.Net 6 - so this is that.
In this post, we’ll walk through the steps necessary to add a basic test to your Asp.Net 6 web site. Note that this is not comprehensive - some dependencies will trip this up (e.g. database access); however, it’s a start. The important thing is that the test will fail where there are basic set-up and configuration issues with the web app.
The Test Project
The first step is to configure a test project. Obviously, your dependencies will vary based on what tools you decide to use, but the following will work for Xunit:
<PackageReference Include="Microsoft.AspNetCore.Mvc.Testing" Version="6.0.5" />
<PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.2.0" />
<PackageReference Include="xunit" Version="2.4.1" />
<PackageReference Include="xunit.runner.console" Version="2.4.1" />
<PackageReference Include="xunit.runner.visualstudio" Version="2.4.5" />
(See this post on Xunit libraries for details on the basic Xunit dependency list for .Net 6.)
The key here is to set-up the Web Application Factory:
var appFactory = new WebApplicationFactory<Program>();
var httpClient = appFactory.CreateClient();
We’ll come back to some specific issues with this exact code shortly, but basically, we’re setting up the in-memory test harness for the service (which in this case, is our web-app). You can obviously do this for an API in exactly the same manner. The rest of our test then looks like this:
using var response = await httpClient.GetAsync("/");
Assert.True(response.IsSuccessStatusCode);
If your test fails, and you want a fighting chance of working out why, you may wish to replace the assertion with this:
var content = await response.Content.ReadAsStringAsync();
That’s basically it; however, as that currently stands, you’ll start getting errors (some that you can see, and some that you cannot). It makes sense to make the HttpClient static, or at least raise it to the class level, as you only need to actually create it once.
Accessing the Main Project
The other issue that you’ll get here is that, because we’re using .Net 6 top level statements in Program.cs, it will tell you that it’s inaccessible. In fact, top level code does generate an implicit class, but it’s internal. This can be worked around my simply adding the following to the end of your Program.cs code:
public partial class Program { } // so you can reference it from tests
(See the references below for details of where this idea came from.)
Summary
In this post, we’ve seen how you can create an integration test that will assert that, at the very least, your web app runs. This method is much faster than constantly having to actually run your project. It obviously makes no assertions about how it runs, and whether what it’s doing is correct.
References
Example of testing top level statements
GitHub Issue reporting error with top level statements being tested
Stack Overflow question on how to access Program.cs from in program using top level statements