Recently on twitter, Clayton asked for a good book about unit testing without mocks. I don’t believe such a thing can be written, so I’ll try to write it in one blog post. First, here it is in one sentence:
Mocks are a smell. They tell you that your code depends on some semi-related part of the system. Rather than work around the design defect, fix the design.
The trick is figuring out what smell you are observing and how to “fix” it. Basically, what alternatives exist. Down the rabbit hole we go. Continue reading “The No Mocks Book”
In the previous post in this series (“last week” to those who didn’t read it over a year ago), I made simple code complicated in the effort to make it unit testable. It was all going along fine, until I started bringing functional programming into the mix.
Since that worked so well, I’m going to demonstrate how I really wrote the code, which brings in functional programming, laziness, and asynchronous programming. Continue reading “Mock Free Example 4: Everything’s Better with Async”
In previous discussions about mock-free unit testing, I’ve shown techniques that I use to eliminate the hard-to-eliminate test doubles. I’ve skipped the simple techniques that I apply all the time. Time to fix that.
One technique eliminated about 90% of the test doubles in my code. It’s simple. It’s been around for a long time. Odds are you already do it but not frequently enough. It even has a name:
Extract Method. Continue reading “Easily Eliminate Most Mocks”
I just published an early relese of my Simulated.FileSystem library. This library makes it easier to separate platform concerns out of my models. It works really well with a hexagonal architecture.
This library will define a set of ports for common external dependencies, with multiple adapters for each port. The initial release just includes a file system port, with two adapters: native file system and in-memory file system. Continue reading “New Simulators Library”
In my character printer, at one point I had some code like this monstrosity. I know it’s a monster, because testing it
- Requires at least one test double (the
- Involves running a bunch of code not related to the unit test at hand.
Many people don’t think this code is so bad. They discuss various ways to test it, usually involving more mocks.
I’m going to show another way. Since it doesn’t require mocks and this is my blog, it’s a better way. Continue reading “Mock Free Example, Part 3: Fixing Untestable Code Sequences”
One of the common uses for mocks is to replace expensive or stateful components, such as file systems, networks, GUIs, and databases.
However, I also see a cluster of other problems that arise at interfaces with these types of components, especially when they are system-level services:
- Primitive obsession. Rarely are these APIs written as methods on an abstract object that return other abstractions. Instead, people pass around a lot of strings & things, which become arguments for static methods.
- State. Partly because there isn’t a place to put it, state tracking becomes a mess. For example, you want to ask a web service for something. Are you logged in? Do you have to do something if you aren’t?
- Lack of encapsulation. Those static methods end up everywhere. And often they end up with duplicate patterns everywhere (e.g., check for login before each call).
- The API does not feel natural to the application. It doesn’t follow the project’s idioms, and doesn’t just flow into place.
For this reason, I use an entirely different sort of test double: a system simulator. And often these simulators stop being test doubles Continue reading “Mock Free Example, part 2: Simulators”
Previously, I presented mocks as nuclear weapons. Unsurprisingly, commenters wanted examples. I exist to serve.
This series will discuss a partly-completed project that I have lying around. The project isn’t perfect. But it will serve to discuss some of the ideas. Since it’s only partly complete, some ideas visible in this stage that would likely become much more subtle with another few days’ work. Or so I hope.
It’s also a full project. The ideas blend into each other at the edges. I am not creating an example to demonstrate an idea; I’m showing how those ideas interact with each other in the wild. This will make the examples more difficult to follow. Sorry. I’ll do my level best to guide you to the areas that I find interesting (whether positive, negative, or simply unfinished).
Continue reading “Mock Free Example, Part 1: Project Intro”
Recently, I’ve had a large number of discussions around the use of mocks for testing, probably because I keep saying that Mocks are Evil.
As a result, I’ve had to articulate how I design systems. Continue reading “Decoupled Design”