This blog post is part of The C# Advent Calendar, a series of 50 posts about C#. Be sure to check out the rest of the blog posts in the calendar! Snapshot testing is a technique that allows you to write tests that assert the state of an object. The object is serialized and stored in a file. The next time the test is run, the serialized object is compared to the existing snapshot file. If the content is… [read more]

ChangeDetection.io is a service that lets you monitor websites and get notified when a change occurs. In an ideal world, all websites would have an RSS feed that you could subscribe to, but unfortunately, this is not the case. Detecting changes could be useful to be notified when a new version of a product is released, or to detect the re-stock of a product. You can use subscribe to <changedetection.io>,… [read more]

MSBuild binary logger allows us to investigate build issues in depth. It records all the events that occur during a build, and it can be replayed to reproduce the build. I've already written about this logger in previous posts: Exploring a MSBuild binary log using the binary log viewer, Detecting Double-Writes in MSBuild using the binlog. By default, the binlog file contains the content of all MSBuild… [read more]

Lambdas can use variables from the enclosing methods (documentation), unless the lambda is static. When a variable is captured, the compiler generates code to create the bridge between the enclosing method and the lambda. Let's consider this simple example: public void M() { var a = 0; // Create a lambda that use "a" from the enclosing method var func = () => Console.WriteLine(a); func(); } When compiling… [read more]

There are formats where you need to read a stream of JsonDocuments separated by a character such as a new line. For instance, you can try to read data from a ndjson response. In this post, I'll show you how to read such a stream. A basic solution would be to split the stream by the separator and then parse each part. However, the JSON document may contain the separator character. For instance, if you use… [read more]

In Roslyn, a SyntaxTree represents the content of a source file. If you need to know the source file that created this SyntaxTree, you can use the FilePath property. This property represents the file path on the disk. But, the file path on the disk may not be what you want. On CI, you should use reproducible builds to get deterministic paths (ContinuousIntegrationBuild=true and <SourceRoot>). In this… [read more]

When you use a record. you can create a new instance by using the new keyword. Or you can copy an instance with some modifications using with expression (non-destructive mutation). The with expression copy all fields from the original instance and then apply the modifications. var john = new Sample("John", "Doe"); var Jane = john with { FirstName = "Jane" }; record Person(string FirstName, string… [read more]

When you use embedded resources in a .NET project, the resource name is computed from the path of the file. By default, it uses a format similar to <Assembly Name>.<File Path>. But the file path doesn't contain a path separator (/ or \). Instead, the path separator is replaced by a dot (.). For example, the resource name for the file resources/index.html is MyAwesomeProject.resources.index.html. So, if… [read more]

Getting the default value of a type at compile time is easy. You can use default(T). What if you want to do the same at runtime? What is the default value for any System.Type? You can find multiple wrong answers on the internet. For example, this one: // ⚠️ Not the same as default(T) object? GetDefaultValue(Type type) => type.IsValueType ? Activator.CreateInstance(type) : null; This works great for… [read more]

You sometimes need to validate that a log message is written to the log. In this post, I describe how to unit test ILogger in .NET Core. There are multiple strategies: You can use a mock framework like Moq to mock the ILogger interface and validate the right calls are made. You can store all logs in-memory and assert the collection. You can use a file logger and assert the log file. Etc. In this post, I… [read more]