The importance of tests in our software
Introduction to unit testing with PHP
Found a typo? Edit meA test is an empirical assertion that demonstrates the behaviour of an expected functionality from something.
Cohn pyramid
There are different test types as we have just seen, even each one is focused on a particular issue from the application.
At the pyramid bottom, the unit tests are accommodated, in the middle the integration ones and on the top the UI tests.
The unit tests should represent the majority of them. Those tests give specific and really fast feedback to the user (50%-60%).
The integration tests are slower than the units and are focused on complex tasks like HTTP requests, database connections, cache operations and other stuff which require some application load (20%-40%).
Lastly, the UI tests at the pyramid top (0%-10%).
Those tests are the most delicate, took a lot of time and they are harder to write and maintain.
- When we said they are delicate, we mean they are too coupled to the source code and a minimal change in the code could provoke a failing test
- They took so much time to be executed; they used to apply a crawler object, which consists of a browser emulator that is capable of seeing the status page, clicking on some buttons, reading any DOM element and so on. Indeed, it is harder to find the failure in an ‘end-to-end’ test because they are unforeseen and took more time
It is not the same legacy as a greenfield project.
Depending on it, those values may vary.
In legacy projects which are really coupled to 3rd party libraries like the database, sometimes it is really hard to write unit tests. The recommendation is to do the inverse, creating first integration tests to check you do not break something and then re-factorize the code with unit tests step by step.
Test Methodologies
Test-Last
This is the worst methodology and sadly the most common.
It happens when you type the tests AFTER you wrote the production code.
Pros:
- At least you have tests (it is dangerous because you can fall into the false sensation of coverage and false positives…)
Cons:
- It is boring because you already have the sensation you are working on something that is already done
Test-First
This methodology is when you type the tests BEFORE you wrote the production code.
Pros:
- This methodology focuses only on green tests
- It is great for integration tests
Cons:
- You do not care so much about a good design of the tests nor the production code
TDD (test-driven development)
This methodology is when you type the tests BEFORE you wrote the production code BUT you are refactoring the code as long as you are working on them.
First, you wrote the test code getting the red light and ONLY then, you work on the implementation to get the green light. Afterwards, you refactor it and so on.
Cons:
- The sensation of slower development
- It requires an important learning curve
- Its implementation is complex in legacy codes
Unit test resources
We use to say “mock” when we want to reference a test double, but there are actually five different types and mock is only one of them.
It can really help you understand what you’re trying to accomplish with your test if you know about what you are doing.
Test doubles
A Test Double is any object that stands in for a real dependency in automated testing. Usually, in PHPUnit, we make test doubles for other classes, but you can also double built-in PHP functions or closures.
The five types of Test Doubles are:
- Dummy — Used only as a placeholder when an argument needs to be filled in
- Stub — Provides fake data to the System Under Test
- Spy — Records information about how it is used and can provide that information back
- Mock — Defines an expectation on how it will be used, and with what parameters. Will cause a test to fail automatically if the expectation isn’t met
- Fake — An actual implementation of the contract, but is unsuitable for production