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Introduction to Writing Unit Tests in PHP with PHPUnit and Docker

Testing your code is a great way to improve quality and minimize bugs due to regression. PHP has a couple frameworks available for unit testing, but the most popular by far is PHPUnit. Because unit tests are going to be run on a variety of environments, running tests within Docker containers can make tests faster and more portable. This tutorial will walk you through setting up a PHP application with unit tests that can be run in Docker.

1. Setting up a PHP Class to Test

First let’s create a simple PHP class in a file called ExampleClass.php:

<?php
class ExampleClass {
    function addOne(int $number): int {
        return $number + 1;
    }
}

This class has one function called addOne that will simply add 1 to an integer when passed in.

2. Installing PHPUnit

Next, let’s install and configure PHPUnit to test this class. Because we’re using Docker, we’ll install PHPUnit via Composer in a container:

docker run --rm -v $(pwd):/app composer/composer:latest require --dev phpunit/phpunit ^6.0

This will install version 6.0 of PHPUnit into our directory’s new vendor folder.

3. Writing a Unit Test

I won’t go into detail on how to write good unit tests, but let’s look at a simple test we might do based on the simple class above:

<?php
use PHPUnit\Framework\TestCase;
class ExampleTest extends TestCase
{
    public function testItCanAddOneToInteger(): void
    {
        $exampleClass = new ExampleClass();
        $input = rand(1, 100);
        $result = $exampleClass->addOne($input);
        $this->assertEquals($input + 1, $result);
    }
}

This test is stored in a file called ExampleTest.php in the same directory as the class we’re testing. Typically, you’ll want to put your application files in a different directory from your tests, but since this is a simple example, everything is in the root directory.

In the function testItCanAddOneToInteger, we instantiate the ExampleClass, get a random number, call the addOne method, and then assert that the result is correct.

4. Running Unit Tests

Finally, to run a unit test you need to make PHPUnit aware of your code files and test files. The best way to do that in a large application is using PHPUnit’s XML configuration file, but since this is a very simple example, we’ll just use the command line interface.

docker run -v $(pwd):/app --rm phpunit/phpunit:latest --bootstrap ExampleClass.php ExampleTest.php

This docker command runs the latest version of PHPUnit and uses the --bootstrap flag to tell it which files it needs. If everything was done correctly, you should see something like this in your terminal output:

PHPUnit 6.0.13 by Sebastian Bergmann, Julien Breux (Docker) and contributors.

.                                                                   1 / 1 (100%)

Time: 77 ms, Memory: 2.00MB

OK (1 test, 1 assertion)

This indicates that one unit test was run and that it passed.

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