PHPUnit needs a phpunit.xml file in order to define the way we want to run the tests. This file defines a set of rules like where the tests are, what code are the tests testing, and so on. Add the following file in your root directory:

<?xml version="1.0" encoding="UTF-8"?>

<phpunit backupGlobals="false"
         backupStaticAttributes="false"
         colors="true"
         convertErrorsToExceptions="true"
         convertNoticesToExceptions="true"
         convertWarningsToExceptions="true"
         processIsolation="false"
         stopOnFailure="false"
         syntaxCheck="false"
         bootstrap="vendor/autoload.php"
>
<testsuites>
<testsuite name="Bookstore Test Suite">
<directory>./tests/</directory>
</testsuite>
</testsuites>
<filter>
<whitelist>
<directory>./src</directory>
</whitelist>
</filter>
</phpunit>

This file defines quite a lot of things. The most important are explained as follows:

When running the tests with PHPUnit, just make sure that you run the command from the same directory where the phpunit.xml file is. We will show you how in the next section.

Right, that's enough preparations and theory; let's write some code. We will write tests for the basic customer, which is a domain object with little logic. First of all, we need to refactor the Unique trait as it still contains some unnecessary code after integrating our application with MySQL. We are talking about the ability to assign the next available ID, which is now handled by the autoincremental field. Remove it, leaving the code as follows:

<?php

namespace BookstoreUtils;

trait Unique {
    protected $id;

    public function setId(int $id) {
        $this->id = $id;
    }

    public function getId(): int {
        return $this->id;
    }
}

The tests will be inside the tests/ directory. The structure of directories should be the same as in the src/ directory so that it is easier to identify where each test should be. The file and the class names need to end with Test so that PHPUnit knows that a file contains tests. Knowing this, our test should be in tests/Domain/Customer/BasicTest.php, as follows:

<?php

namespace BookstoreTestsDomainCustomer;

use BookstoreDomainCustomerBasic;
use PHPUnit_Framework_TestCase;

class BasicTest extends PHPUnit_Framework_TestCase {
    public function testAmountToBorrow() {
        $customer = new Basic(1, 'han', 'solo', '[email protected]');

        $this->assertSame(
            3,
            $customer->getAmountToBorrow(),
            'Basic customer should borrow up to 3 books.'
        );
    }
}

As you can note, the BasicTest class extends from PHPUnit_Framework_TestCase. All test classes have to extend from this class. This class comes with a set of methods that allow you to make assertions. An assertion in PHPUnit is just a check performed on a value. Assertions can be comparisons to other values, a verification of some attributes of the values, and so on. If an assertion is not true, the test will be marked as failed, outputting the proper error message to the developer. The example shows an assertion using the assertSame method, which will compare two values, expecting that both of them are exactly the same. The third argument is an error message that the assertion will show in case it fails.

Also, note that the function names that start with test are the ones executed with PHPUnit. In this example, we have one unique test named testAmountToBorrow that instantiates a basic customer and verifies that the amount of books that the customer can borrow is 3. In the next section, we will show you how to run this test and get feedback from it.

Optionally, you could use any function name if you add the @test annotation in the method's DocBlock, as follows:

/**
 * @test
 */
public function thisIsATestToo() {
  //...
}

In order to run the tests you wrote, you need to execute the script that Composer generated in vendor/bin. Remember always to run from the root directory of the project so that PHPUnit can find your phpunit.xml configuration file. Then, type ./vendor/bin/phpunit.

When executing this program, we will get the feedback given by the tests. The output shows us that there is one test (one method) and one assertion and whether these were satisfactory. This output is what you would like to see every time you run your tests, but you will get more failed tests than you would like. Let's take a look at them by adding the following test:

public function testFail() {
    $customer = new Basic(1, 'han', 'solo', '[email protected]');

    $this->assertSame(
        4,
        $customer->getAmountToBorrow(),
        'Basic customer should borrow up to 3 books.'
    );
}

This test will fail as we are checking whether getAmountToBorrow returns 4, but you know that it always returns 3. Let's run the tests and take a look at what kind of output we get.

We can quickly note that the output is not good due to the red color. It shows us that there is a failure, pointing to the class and test method that failed. The feedback points out the type of failure (as 3 is not identical to 4) and optionally, the error message we added when invoking the assert method.