This repository gives a simple example as to how to test log output in an integration test for an ASP.NET Core API. It is a working example for my blog post Testing Logging in ASP.NET Core, which gives a background and explanation of the code in this repository.
The Api project contains a simple API setup with one /test endpoint that logs an error level. The Test project contains an ILoggerProvider implementation to capture logs and expose them in a way that the tests can easily read. The single Test.TestErrorLogged test demonstrates how to inject the test logger into the host when setting up a WebApplicationFactory.
In order to run, you'll need to ensure you have the .NET 9 SDK installed.
To run in Visual Studio, open the SLN, build, navigate to the Test Explorer, and execute the test.
To run in VS Code, I recommend installing the C# Dev Kit extension. With that extension, you can open the folder containing the project, build with dotnet, then navigate to the Testing view to execute the test.