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Lab - Characterization Tests
Daunted by unfamiliar legacy code? Let's practice
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About Author
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Facundo is a Cloud Solutions Architect at New Signature. He enjoys helping clients with architecture, containers/orchestration, and stream lining development processes.
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Getting Started
/getting-started
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Unit Tests
/lab-unit-tests

Overview

You've been tasked with creating a new feature. Clearly, the code is not in the best shape. So you decide you want to do some refactoring and add automated tests. Nice! the boyscout rule - leaving things better than you found them.

Before we start creating the feature, let's create some characterization tests. Characterization tests help us learn from the system and how it's currently in production. This is extremely useful when learning what a system does and how it works. If you'd like a refresher on characterization tests, there's a really good blog post from Michael Feathers.

Useful Links

Write Characterization Tests

Become familiar with the code. Don't refactor. Let's start with a single method and be inquisitive.

Start with ProductsController.Get

Feel free to create a test project. Start experimenting and creating a characterization test to understand how it works today.

As you start learning, create some test cases to start documenting given some criteria what the expected results are.

Note: If you are new to ASP.NET Core, when you create a test project, make sure it is in .NET Core and it uses Microsoft.AspNetCore.App NuGet package

Note: Remember, don't start refactoring right away. You have running database using docker. Feel free to connect to it using your tests and expirement away.

How do I know I'm done?

  • Do you have a good idea about the kind of refactorings you'd to do to start breaking dependencies?
  • What would it take to start making this code more unit testable?
  • Do you comfortable enough to start refactoring without breaking it?

Refactor

Create an end-state in mind of what you would like the architecture to look like. For example, what would the code look like if it was using:

  • Dependency Injection
  • SOLID Principles
  • Clean Architecture

Don't Forget: Run your characterization tests often to make sure your refactoring is not breaking things.

Checkout the Resources tab for useful links.

Stretch Goal

  • What happens when the database goes down? Can you similate this?
  • Write some characterization tests for ProductsController.Consume
  • Refactor with what you're comfortable