webservice-mocking.md

Mocking SOAP Webservices with Phockito and Behat

Overview

Web applications typically don't live in isolation: They provide data to third parties, as well as consume data from other services, and often even write back to those services. SOAP is a common web service layer to achieve this level of interaction.

Web services have a couple of disadvantages when it comes to testing though:

• They're slow down our tests, responding in seconds rather than milliseconds
• Their data can change over time, making it hard to start with a clean slate
• They're not isolated, meaning multiple test runs accessing a webservice in parallel can cause side effects for each other
• Since their data isn't defined in our tests, its hard to understand the assumptions and requirements of a test.

This is where mocks objects come in, which replace the "real" webservice with a fake data defined in our test framework. The challenge is to get mocks defined as in-memory objects via PHP while executing Behat steps on the commandline, but applying those same mocks in a different process when Behat/Mink/Selenium perform a web request. That's solved by generated PHP code which is included as part of the bootstrap process.

There's several parts to this:

• Behat parses features into executable steps
• Mink interacts with Selenium to remote control a browser
• PHP's built-in SoapClient is used for the "real" API connection
• A "gateway" class which encapsulates the SOAP interactions
• Phockito as a mocking framework to "hardcode" method returns
• The TestSessionStubCodeWriter which writes PHP code to be included only in test runs. In our case it contains Phockito mock object definitions.

Example: A Currency Conversion Rate Viewer

How the pieces fit together is best illustrated as an example. We'll create a currency rate viewer, based on a free online webservice. The example assumes you have a basic knowledge of Behat and the Behat SilverStripe extension. Let's explain the feature through the Gherkin language as Behat steps:

Feature:
	As a website visitor
	I want to see currency conversion rates
	In order to decide whether its worth buying

	Scenario: View conversion rates on homepage
		Given I have a currency rate from "NZD" to "EUR" of "1.56"
		And I go to "/convert?from=NZD&to=EUR"
		Then I should see "NZD -> EUR: 1.56"

Follow the Behat+SilverStripe installation instructions, then install the Phockito mocking framework:

composer require hafriedlander/phockito:*

First we'll create a CurrencyGateway class which encapsulates a SoapClient through the gateyway design pattern. It wraps each SOAP method in its own method, reading and writing native PHP types such as arrays and integers. This decouples the business logic from the underlying service layer, and allows us to mock the return values later without requiring access to the live webservice.

// mysite/code/CurrencyGateway.php
class CurrencyGateway {
	protected $client;

	function __construct($client = null) {
		$this->client = new SoapClient('http://www.webservicex.net/CurrencyConvertor.asmx?WSDL');
	}

	function convert($from, $to) {
		return $this->client->ConversionRate($from, $to);
	}
}

The controller logic for this is really simple. We'll stick to request parameters and plaintext responses just to keep the code manageable, a more realistic controller would likely use a form and HTML formatted responses. Its important that our CurrencyGateway is instanciated through the use of dependency injection, so we can replace its implementation with a mock object later.

// mysite/code/MyController.php
class ConvertController extends Controller {
	function index($request) {
		$gateway = Injector::inst()->get('CurrencyGateway');
		$from = $request->getVar('from');
		$to = $request->getVar('to');
		$rate = $gateway->convert($from, $to);
		$this->response->addHeader('Content-Type', 'text/plain');
		return "$from -> $to: $rate";
	}
}

The controller needs to be hooked up to a route (in mysite/_config/_config.yml):

Director:
  rules:
    'convert/$Action': 'ConvertController'

If you haven't already, now's the time to initialize your Behat tests through a call to vendor/bin/behat --init @mysite. Copy the feature steps from above into a new mysite/tests/behat/features/view-rates.feature file. Open the already generated FeatureContext.php file and add the following code.

// mysite/tests/behat/features/bootstrap/Context/FeatureContext.php
use namespace SilverStripe\TestSession\TestSessionStubCodeWriter;
class FeatureContext extends SilverStripeContext {

	protected $stubCodeWriter;

	public function __construct() {
		// ...

		$this->stubCodeWriter = Injector::inst()->get(TestSessionStubCodeWriter::class);
	}

	/**
	 * @BeforeScenario
	 */
	public function initTestSessionStubCode() {
		$php = <<<PHP
\$mock = Phockito::mock('CurrencyGateway');
Injector::inst()->registerService(\$mock, 'CurrencyGateway');
PHP;
		$this->stubCodeWriter->write($php);
	}

	/**
	 * @AfterScenario
	 */
	public function resetTestSessionStubCode() {
		$this->stubCodeWriter->reset();
	}

	public function getTestSessionState() {
		return array_merge(
			parent::getTestSessionState(),
			array('stubfile' => $this->stubCodeWriter->getFilePath())
		);
	}

	/**
	 * @Given /^I have a currency rate from "([^"]*)" to "([^"]*)" of "([^"]*)"$/
	 */
	public function stepGivenACurrency($from, $to, $rate) {
		$php = <<<PHP
Phockito::when(\$mock->convert('$from','$to'))->return($rate);
PHP;
		$writer->write($php);
	}
}

The TestSessionStubCodeWriter takes care of writing out PHP to a specified file. It defaults to testSessionStubCode.php inside your webroot. The file only lives for the duration of a test session, and is regenerated for each scenario to avoid side effects (hence the methods tagged with @BeforeScenario and @AfterScenario).

A useful pattern here is to set up objects via @BeforeScenario, in our case a mock gateway in initTestSessionStubCode(). This object can be used in later step definitions like stepGivenACurrency() to mock webservice responses without any further setup or duplication.

The generated code which is executed on every web request reads:

<?php
$mock = Phockito::mock('CurrencyGateway');
Injector::inst()->registerService($mock, 'CurrencyGateway');
Phockito::when($mock->convert('EUR','NZD'))->return(1.56);

Keep in mind escaping rules for PHP when placed in a heredoc block: Variables are resolved when the string is constructed, unless escaped with a backslash.

The test session started in your browser by Selenium/Behat needs to know which file to include, which is handled by the getTestSessionState() method.