In a previous article, we discussed “persistence” and “time” as boundary concepts that need mocking by means of dependency inversion: define your own interface, then provide an implementation for it. There were three other topics left to cover: the filesystem, the network and randomness.

Mocking the filesystem

We already covered “persistence”, but only in the sense that we sometimes need a way to make in-memory objects persistent. After a restart of the application we should be able to bring back those objects and continue to use them as if nothing happened.

I read this tweet:

"The object-oriented version of spaghetti code is, of course, 'lasagna code'. Too many layers." - Roberto Waltman

— Programming Wisdom (@CodeWisdom) February 24, 2018

Jokes taken as advice

It’s not the first time I’d heard of this quote. Somehow it annoys me, not just this one joke, but many jokes like this one. I know I should be laughing, but I’m always worried about jokes like this going to be interpreted as advice, in its most extreme form. E.g. the advice distilled from this tweet could be: “Layers? Don’t go there. Before you know it, you have lasagna code…”

More and more I’ve come to realize that I’ve been mocking less and less.

The thing is, creating test doubles is a very dangerous activity. For example, what I often see is something like this:

$entityManager = $this->createMock(EntityManager::class);

$entityManager->expects($this->once())
    ->method('persist')
    ->with($object);
$entityManager->expects($this->once())
    ->method('flush')
    ->with($object);

Or, what appears to be better, since we’d be mocking an interface instead of a concrete class:

$entityManager = $this->createMock(ObjectManagerInterface::class);
// ...

To be very honest, there isn’t a big different between these two examples. If this code is in, for example, a unit test for a repository class, we’re not testing many of the aspects of the code that should have been tested instead.

Why code coverage for Behat?

PHPUnit has built-in several options for generating code coverage data and reports. Behat doesn’t. As Konstantin Kudryashov (@everzet) points out in an issue asking for code coverage options in Behat:

Code coverage is controversial idea and code coverage for StoryBDD framework is just nonsense. If you’re doing code testing with StoryBDD - you’re doing it wrong.

He’s right I guess. The main issue is that StoryBDD isn’t about code, so it doesn’t make sense to calculate code coverage for it. Furthermore, the danger of collecting code coverage data and generating coverage reports is that people will start using it as a metric for code quality. And maybe they’ll even set management targets based on coverage percentage. Anyway, that’s not what this article is about…

A little background: speakers don’t get paid

Speakers like myself don’t get paid for doing a talk at a tech conference. That’s why I call this work “open source”. People will get a video or audio recording of the talk, including separately viewable or downloadable slides for free. The idea is, a conference costs a lot of money to organise. It is quite expensive to fly in all those speakers. So there’s no money to pay the speakers for all their work (for me personally it’s about 80 hours of preparation, plus time spent travelling, usually half a day before and after the conference). Speakers get their travel costs reimbursed, they often get two nights at a hotel, and a ticket to the conference. Plus, they get advertising for their personal brand (increasing their reputation as an expert, a funny person, or just a person with more Google results for their name).

This article continues where Unary call sites and intention-revealing interfaces ended.

While reading David West’s excellent book “Object Thinking”, I stumbled across an interesting quote from David Parnas on the programming method that most of us use by default:

The easiest way to describe the programming method used in most projects today was given to me by a teacher who was explaining how he teaches programming. “Think like a computer,” he said. He instructed his students to begin by thinking about what the computer had to do first and to write that down. They would then think about what the computer had to do next and continue in that way until they had described the last thing the computer would do… […]

Call sites

One of the features I love most about my IDE is the button “Find Usages”. It is invaluable when improving a legacy code base. When used on a class it will show you where this class is used (as a parameter type, in an import statement, etc.). When used on a method, it will show you where this method gets called. Users of a method are often called “clients”, but when we use “Find Usages”, we might as well use the more generic term “call sites”.

Setting the stage: Code complexity

Code complexity often gets measured by calculating the Cyclomatic Complexity per unit of code. The number can be calculated by taking all the branches of the code into consideration.

Code complexity is an indicator for several things:

• How hard it is to understand a piece of code; a high number indicates many branches in the code. When reading the code, a programmer has to keep track of all those branches, in order to understand all the different ways in which the code can work.
• How hard it is to test that piece of code; a high number indicates many branches in the code, and in order to fully test the piece of code, all those branches need to be covered separately.

In both cases, high code complexity is a really bad thing. So, in general, we always strive for low code complexity. Unfortunately, many projects that you’ll inherit (“legacy projects”), will contain code that has high code complexity, and no tests. A common hypothesis is that a high code complexity arises from a lack of tests. At the same time, it’s really hard to write tests for code with high complexity, so this is a situation that is really hard to get out.

CQRS - not a complicated thing

CQRS has some reputation issues. Mainly, people will feel that it’s too complicated to apply in their current projects. It will often be considered over-engineering. I think CQRS is simply misunderstood, which is the reason many people will not choose it as a design technique. One of the common misconceptions is that CQRS always goes together with event sourcing, which is indeed more costly and risky to implement.

Today I’m happy to release my latest book, “Microservices for everyone”! 90% of it was done in July but you know what happens with almost-finished projects: they remain almost-finished for a long time. I did some useful things though, like preparing a print edition of the book.

Foreword

Finally, and I’m very proud of that, I received Vaughn Vernon’s foreword for this book. You may know Vaughn as the author of “Implementing Domain-Driven Design”. It made a lot of sense to ask him to write the foreword, since many of the ideas behind microservice architecture can be traced back to messaging and integration patterns, and Domain-Driven Design. Vaughn is an expert in all of these topics, and it was only to be expected of him to write an excellent foreword.