In our last post, we took a basic look at testing your code in WordPress. Today, we’re going to take another step towards writing well-tested code, by introducing you to (and helping you understand) all the jargon that gets thrown around when you talk about unit testing for WordPress.
Types of Tests
Yup, unit tests are not the only types of tests we can have for our application so let’s look at the different types of tests you may use in your work.
These types of tests are the first stage in a testing system. They specifically test to ensure that the code you wrote performs as expected. Unit tests form the foundation of your tests because if your code doesn’t work properly, then later types of tests are built on a shaky foundation.
If I wanted to limit the editing of permalinks to site administrators for posts that are over two weeks old my unit test would use WP_Mock to ensure that I have a user of the proper type and a post with the proper date. Then I’d make sure that my function returned the expected true or false value.
Unit tests should have no dependencies outside of the code you’ve written. They should interact with no other system. That means our last post wasn’t a true unit test, it was an integration test because we interacted with the database as we created our user.
When you use unit tests as the foundation of your work, you help ensure that each method/function has a single responsibility because it gets progressively harder to test as you add more conditions to a single function.
Some of the tools you’ll encounter in unit testing WordPress projects are:
This is the second type of testing you’ll do in your work. Integration tests make sure that the interactions between two systems function as expected. Unlike unit tests, the goal here is to see the interaction between multiple systems.
WordPress itself does more integration tests than unit tests because when most of the application was written best practices were different. The functions inside WordPress are much larger than many newer PHP CMS’s and do much more work. These bigger functions are hard to unit test properly because they do so much. That means we rely more on integration testing as we check how our code directly works with WordPress.
None of this is bad, it’s simply a product of an application that wasn’t built when testing was as common as it is now.
Another example of an integration test would be if you were building an integration with an email marketing platform. You may use unit tests to make sure you validate the email properly, and submit the form as expected. Integration tests would be used to ensure that when you submit your valid email to the email platform you deal with the response properly.
Tools for integration testing:
Mutation testing is only going to be used for projects that have some sort of test coverage already. This type of testing creates “mutants” of your code by introducing common coding errors. The goal is that your unit tests break when these errors are introduced which means you’ve caught and killed the mutant. Mutation testing tools will report back on how many mutants you’ve killed and the places in which you haven’t caught mutants.
Mutation testing can be used to measure the quality of your test coverage. If you’ve got lots of mutants alongside 100% testing coverage, you have a big problem. This means that your tests don’t catch common errors programmers make. You’ve got code breakage waiting to happen.
Essentially, you’re testing your tests.
Tools for mutation testing:
These can also be called functional test or browser testing. Where unit tests start with your code and work outwards, acceptance tests take the view of the person using your software. With acceptance tests, you may automate the web browser to interact with your site to make sure that users see what they expect to see.
Acceptance tests are harder to maintain because a small wording change in the UI of your software can mean that the test breaks because the automation can no longer find the UI elements it expects to find. For that reason, only invest in acceptance tests for business-critical infrastructure, like the checkout process on your shopping cart.
Tools for acceptance testing:
Now that we’ve covered the types of tests you can do, we need to make sure we understand the other language that developers will use as they write tests.
The term test doubles is a generic term that refers to any time you replace a production object/function/thing for testing purposes. We did this in our previous post on Getting Started with Unit Testing in WordPress when we used WP_UnitTestCase to add a user that didn’t exist in our production database. It can be helpful to think of it like a stunt double who “stands in” for the actor when things get dangerous. Test doubles “stand-in” for our data and code to make testing easier. They should look and behave like their production counterparts but be simplified to reduce complexity when we’re testing.
Mocks are used when you don’t want to interact with the API or database. You use a mock to fake database interactions so you can test a single unit of code without adding the complexity of a database.
A mock doesn’t have to be data in a database. A tool like WP_Mock has the ability to fake the hook system inside WordPress. This lets you test to see if a hook was called in your function, without needing to interact with WordPress itself.
Below we can see an example in WP_Mock where we fake the get_permalink function. We provide the number of times we expect the function to be called, arguments we expect, and the value we expect returned.
\WPMock::userFunction( 'getpermalink', array(
'args' => 42,
'times' => 1,
'return' => 'https://theanswertoeverything.fourtytwo/guide
We’ll cover how to use WP_Mock in a future post.
Stubs are hard coded values for our tests, like canned answers to the questions our test may ask. You would be using a stub if you instructed your test to assume that a user is logged in while running a test. Another test may assume that the user is logged out. Both tests would be making sure that your functions returned the proper values for the given branch in your code.
It’s very likely that you’re using stubs and mocks together. In the example above, you use a stub to assume the logged in value, and then a mock to make sure that the proper values are returned.
Test dummies are used when you don’t care about what the code does. Maybe you use a dummy to fill in an array or parameter list so that the code works properly. Stubs are extra information that likely doesn’t matter in the context of the specific test you’re writing.
For a logged-in user, maybe part of the function your testing expects a name. Even if your current test doesn’t need that name, you need to make sure it’s filled in so that your test passes. Of course, you should also test the result of your function without that name so you’re sure that you handle failure conditions properly.
A factory is a tool that lets us populate valid objects in our data model so that we can test the data. In our last case we used a factory when we added a user to our code inside WP_UnitTestCase.
One thing to be wary of here is changing the data model in your code. If your user suddenly needs an extra field, then you’ll need to head into every test and make sure that you have added that extra field every time you’ve used a factory.
This is a catch-all term for dynamically replacing attributes and functions at runtime. WP_Mock is “monkey patching” by replacing the default WordPress functions for testing. This means that we don’t have to call into WordPress directly when we’re unit testing.
An assertion is a boolean value which will be true unless there is an error. An example would be using assertFileEquals to check if a file has the expected content. It will return true if the file matches expectations, and you have a passing test.
BDD or TDD?
Now, what overall system are you going to approach your tests with? Does it matter more that individual functions are valid, or that the behavior the end-user sees is valid?
TDD or Test Driven Development is when you write tests to validate that the code functions as expected. Like unit tests, you’re starting with the expectation of the code and then working towards the customer/user as you go. TDD doesn’t care about the outputs, it’s only concerned that the tests function as expected.
Tests written under TDD are only going to be readable by developers that understand testing and what an assertion means.
BDD or Behavior Driven Development grew out of the shortcomings of TDD. Here you start with what the end-user expects to happen as a result of the code. You still write your tests first, but you focus them on the result of your code. BDD doesn’t care how you arrive at outputs, as long as the expected behavior is the result.
One big benefit to BDD tools like Cucumber is that the language used to write the test is easily readable by customers and developers. It’s easy enough to understand that customers can write feature requests using Cucumber after a brief introduction.
Now, which one should you use? The correct answer is probably a bit of both. TDD methods can be used to ensure that the code the developer writes runs as expected. BDD can be used to make sure that the output of that code is what the customer expects to happen.
That’s all, folks! Understanding unit testing for WordPress just got a lot easier. With all that jargon under your belt, you’ll be ready for the next post where we’ll build a plugin using TDD and BDD with all the tools at our disposal.