Dependency injection: the good and the bad Dependency injection (DI) is a great pattern, which can really help make your code cleaner, more decoupled and more testable. There are many DI libraries, like Autofac, Lamar (StructureMap’s successor), Castle Windsor, etc., but lately I’ve mostly been using the one provided by Microsoft in .NET Core : Microsoft.Extensions.DependencyInjection. It’s not the most full-featured (in fact, it’s pretty bare-bones), but I find it sufficient in most cases.
Most JSON converters are fairly simple, and typically self-contained. But once in a while, you need to do something a little more complex in a converter, and you end up needing to call a service. However, there’s no built-in dependency injection in System.Text.Json converters… How can you access the service you need? There are basically two variants of this problem. One has a simple solution, the other is a bit of a hack…
The problem with circular dependencies When building an application, good design dictates that you should avoid circular dependencies between your services. A circular dependency is when some components depend on each other, directly or indirectly, e.g. A depends on B which depends on C which depends on A: It is generally agreed that this should be avoided; I won’t go into the details of the conceptual and theoretical reasons, because there are plenty of resources about it on the web.
Today I’d like to share a nice feature I discovered recently in FakeItEasy. When you write unit tests for a class that takes dependencies, you typically need to create fake/mock dependencies and manually inject them into the SUT (System Under Test), or use a DI container to register the fake dependencies and construct the SUT. This is a bit tedious, and a few months ago I came up with an auto-mocking Unity extension to make it easier.
Unit testing can be tedious sometimes, especially when testing classes that have complex dependencies. Fortunately, some tools make it somewhat easier. I’ve been using FakeItEasy a lot recently; it’s a very easy to use mocking framework for .NET. It has a very lean and simple API based on generics and lambda expressions, and is a real pleasure to work with. It came as a breath of fresh air compared to the old RhinoMocks I had been using before.