Maxi ContieriObjects work fine and fulfill business objectives. But we need to test them. Let's break them.
TL;DR: Don't write methods with the only purpose of being used in your tests.
Problems
Encapsulation Violation.
Bad interfaces
Coupling
Solutions
Don't break encapsulation.
Test must be in full control.
If you cannot control your object, you are coupled. Decouple them!
Sample Code
Wrong
<?
class Hangman {
private $wordToGuess;
function __construct() {
$this->wordToGuess = getRandomWord();
//Test is not in control of this
}
public function getWordToGuess(): string {
return $this->wordToGuess;
}
}
class HangmanTest extends TestCase {
function test01WordIsGuessed() {
$hangmanGame = new Hangman();
$this->assertEquals('tests', $hangmanGame->wordToGuess());
//how can we make sure the word is guessed?
}
}
Right
<?
class Hangman {
private $wordToGuess;
function __construct(WordRandomizer $wordRandomizer) {
$this->wordToGuess = $wordRandomizer->newRandomWord();
}
}
class MockRandomizer implements WordRandomizer {
function newRandomWord(){
return 'tests';
}
}
class HangmanTest extends TestCase {
function test01WordIsGuessed() {
$hangmanGame = new Hangman(new MockRandomizer());
$this->assertFalse($hangmanGame->wordWasGuessed());
$hangmanGame->play('t');
$this->assertFalse($hangmanGame->wordWasGuessed());
$hangmanGame->play('e');
$this->assertFalse($hangmanGame->wordWasGuessed());
$hangmanGame->play('s');
$this->assertTrue($hangmanGame->wordWasGuessed());
//We just test behavior
}
}
Detection
This is a design smell.
We can detect we need a method just for test.
Tags
- Information Hiding
Conclusion
White-box tests are fragile. They test implementation instead of behavior.
Relations
More Info
Credits
This smell was inspired by @Rodrigo
Nothing makes a system more flexible than a suite of tests.
Robert Martin
This article is part of the CodeSmell Series.
