Chapter 3. PHPUnit's Goals

So far, we only have two tests for the Array built-in and the sizeof( ) function. When we start to test the numerous array_*( ) functions PHP offers, we will need to write a test for each of them. We could write all these tests from scratch. However, it is much better to write a testing infrastructure once and then write only the unique parts of each test. PHPUnit is such an infrastructure.

Example 5 shows how we have to rewrite our two tests from Example 4 so that we can use them with PHPUnit.

Example 5. Testing Array and sizeof( ) with PHPUnit

<?php
require_once 'PHPUnit2/Framework/TestCase.php';

class ArrayTest extends PHPUnit2_Framework_TestCase {
  public function testNewArrayIsEmpty( ) {
    // Create the Array fixture.
    $fixture = Array( );

    // Assert that the size of the Array fixture is 0. 
    $this->assertEquals(0, sizeof($fixture)); 
  }
  public function testArrayContainsAnElement( ) { 
    // Create the Array fixture.    
		$fixture = Array( );

    // Add an element to the Array fixture.    
		$fixture[] = 'Element';
 
		// Assert that the size of the Array fixture is 1. 
		$this->assertEquals(1, sizeof($fixture));
  }
}
?>

Example 5 shows the basic steps for writing tests with PHPUnit:

The tests for a class Class go into a class ClassTest.
ClassTest inherits (most of the time) from PHPUnit2_ Framework_TestCase.
The tests are public methods that expect no parameters and are named test*.
Inside the test methods, assertion methods such as assertEquals( ) (see Table 6) are used to assert that an actual value matches an expected value.

A framework such as PHPUnit has to resolve a set of constraints, some of which seem to conflict with each other. Simultaneously, tests should be:

Easy to learn to write.: Tests should be easy to learn to write; otherwise, developers will not learn to write them.
Easy to write.: Tests should be easy to write; otherwise, developers will not write them.
Easy to read.: Test code should contain no extraneous overhead so that the test itself does not get lost in the noise that surrounds it.
Easy to execute.: Tests should run at the touch of a button and present their results in a clear and unambiguous format.
Quick to execute.: Tests should run fast so they can be run hundreds or thousands of times a day.
Isolated.: Tests should not affect each other. If the order in which the tests are run changes, the results of the tests should not change.
Composable.: We should be able to run any number or combination of tests together. This is a corollary of isolation.

There are two main clashes within this group of constraints:

Easy to learn to write versus easy to write.: Tests do not generally require all the flexibility of a programming language. Many testing tools provide their own scripting language that includes only the minimum necessary features for writing tests. The resulting tests are easy to read and write because they have no noise to distract you from the content of the tests. However, learning yet another programming language and set of programming tools is inconvenient and clutters the mind.
Isolated versus quick to execute.: If you want the results of one test not to affect the results of another test, each test should create the full state of the testing before it begins to execute, and return the world to its original state when it finishes. However, setting it up can take a long time (e.g., connecting to a database and initializing it to a known state using realistic data).

PHPUnit attempts to resolve these conflicts by using PHP as the testing language. Sometimes the full power of PHP is overkill for writing short, straight-line tests, but by using PHP, we leverage all the experience and tools programmers already have in place. Because we are trying to convince reluctant testers, lowering the barrier to writing those initial tests is particularly important.

PHPUnit errs on the side of isolation over quick execution. Isolated tests are valuable because they provide high-quality feedback. You do not get a report with a bunch of test failures that were really caused because one test at the beginning of the suite failed and left the world messed up for the rest of the tests. This orientation toward isolated tests encourages designs with a large number of simple objects. Each object can be tested quickly in isolation. The result is better designs and faster tests.

PHPUnit assumes that most tests succeed, and it is not worth reporting the details of successful tests. When a test fails, that fact is worth noting and reporting. The vast majority of tests should succeed and are not worth commenting on, except to count the number of tests that run. This is an assumption that is really built into the reporting classes and not into the core of PHPUnit. When the results of a test run are reported, you see how many tests were executed, but you only see details for those that failed.

Tests are expected to be fine-grained, testing one aspect of one object. Hence, the first time a test fails, execution of the test halts, and PHPUnit reports the failure. It is an art to test by running many small tests. Fine-grained tests improve the overall design of the system.

When you test an object with PHPUnit, you do so only through the object's public interface. Testing based only on publicly visible behavior encourages you to confront and solve difficult design problems before the results of poor design can affect large parts of the system.

Table of Contents