Decouple or mock? - php

Question

Suppose I have this class:
class SomeClass
{
// Top level function
public function execute($command)
{
// Get output from system tool
$output = $this->runTool($command);
// Check output for errors
if ($this->hasError($output))
return false;
// And parse success response from tool
return $this->parseOutput($output);
}
// There we're make a call to system
private function runTool($command)
{
return `/some/system/tool $command`;
}
[...]
}
I do not want to run system tool in my test, I want to replace a system call with predefined output.
So, the question is - should I create another class, move system call in it and mock that class in the test, or I can mock only that function of class which I will test?
Sure, both approaches will work, but which of them will be serve testing purposes better?

Answer 1

If you follow the single responsibility principle, you won't have this problem. Your class does not need to know how system calls are made, so you will have to use another class. You mock that.
IMO, in most cases when you need to mock protected or private methods, they do stuff that should be into another class and be mocked.

Answer 2

I would say it really depends on your infrastructure. Sometimes it is better to use Mock, sometimes Stub.
If the case is, that the class you want to test contains this unwanted method - use Mock and mock only this one function. That will make you sure, that any changes made to that class will be handled by the test.
If the unwanted function is a part of i.e. injected service or another class, which is not the domain of this particular test, you can create a stub.

Answer 3

You can't test private method, you can use a workaround and invoke it via reflection as described in this article and discussed in this SO QUESTION
But i suggest you to change the method visibility to protected and mock only the behaviour of the runTool method.
As example, suppose the following modified version of your class (i don't know how other method work so i suppose that you want to test their behaviour and take this implementation as example):
<?php
namespace Acme\DemoBundle\Service;
class SomeClass
{
// Top level function
public function execute($command)
{
// Get output from system tool
$output = $this->runTool($command);
// Check output for errors
if ($this->hasError($output))
return false;
// And parse success response from tool
return $this->parseOutput($output);
}
// There we're make a call to system
protected function runTool($command)
{
return `/some/system/tool $command`;
}
private function hasError($output)
{
return $output == "error";
}
private function parseOutput($output)
{
return json_decode($output);
}
}
As suppose the following test case:
<?php
namespace Acme\DemoBundle\Tests;
class SomeClassTest extends \PHPUnit_Framework_TestCase {
public function testCommandReturnError()
{
$mock = $this->getMockBuilder('Acme\DemoBundle\Service\SomeClass')
->setMethods(array('runTool'))
->disableOriginalConstructor()
->getMock()
;
$mock
->expects($this->exactly(1))
->method('runTool')
->with("commandName")
->will($this->returnValue("error"));
$this->assertFalse($mock->execute("commandName"));
}
public function testCommandReturnCorrectValue()
{
$mock = $this->getMockBuilder('Acme\DemoBundle\Service\SomeClass')
->setMethods(array('runTool'))
->disableOriginalConstructor()
->getMock()
;
$mock
->expects($this->exactly(1))
->method('runTool')
->with("commandName")
->will($this->returnValue('{"title":"myTitle"}'));
$returnValue = $mock->execute("commandName");
$this->assertEquals("myTitle", $returnValue->title);
}
}
Hope this help