Stub is the next simplest test double after the Dummy.

It doesn't have any expectations about the object behavior, but behaves in a specific way when put in a specific environment.

Below is the class under the test:

<?php

namespace App;

class Questioner
{
    private $output;
    private $questions = [];

    public function __construct(OutputInterface $output)
    {
        $this->output = $output;
    }

    /** @return int */
    public function getQuestionsCount()
    {
        return 0;
    }

    /**
     * Save under a new name.
     *
     * @param  string $name
     * @return boolean
     */
    public function saveAs($name)
    {
        return $this->output->save($this->questions, $name);
    }
}

saveAs method can be tested by using a stub test double:

<?php

namespace tests;

use App\Output;
use App\Questioner;

class QuestionerTest extends \PHPUnit_Framework_TestCase
{
    /**
     * @test
     */
    function new_questioner_has_no_questions()
    {
        $outputDummy = $this->prophesize(Output::class);
        $questioner  = new Questioner($outputDummy->reveal());

        $this->assertSame(0, $questioner->getQuestionsCount());
    }

    /**
     * @test
     */
    function questioner_is_saved_under_a_new_name()
    {
        $outputStub = $this->prophesize(Output::class);
        $outputStub->save([], 'new name')->willReturn(true);
        $questioner = new Questioner($outputStub->reveal());

        $this->assertTrue($questioner->saveAs('new name'));
    }
}

The test will pass as long as first parameter for save method is an empty array ([]) and the second parameter is new name. Prophecy allows you to use argument wildcards making your tests more durable. Below you can see a new test which allows any string for a name:

<?php

// ...
use Prophecy\Argument;

class QuestionerTest extends \PHPUnit_Framework_TestCase
{
    // ...

    /**
     * @test
     */
    function questioner_is_saved_under_any_name()
    {
        $outputStub = $this->prophesize(Output::class);
        $outputStub->save([], Argument::type('string'))->willReturn(true);
        $questioner = new Questioner($outputStub->reveal());

        $this->assertTrue($questioner->saveAs('any name'));
    }
}

For the full list of arguments you can you check the code of Prophecy\Argument class. Here's some of them you might want to use in your tests:

• Argument::is($value) checks that the argument is identical to a specific value
• Argument::exact($value) checks that the arguments matches a specific value
• Argument::type($typeOrClass) checks that the argument matches a specific type or class name
• Argument::any() matches any argument

This article is from the Test doubles using Prophecy series which is made from following articles:

Dummy Test Double Using Prophecy

Stub Test Double Using Prophecy

Spy Test Double Using Prophecy

Mock Test Double Using Prophecy

Fake Test Double Using Prophecy