Presentation on mocking dependencies in PHPUnit

1. Mocking Dependencies in
PHPUnit
Matt Frost · IRC: mfrost503 · Feedback: http://joind.in/8693

2. We’ll be covering
✤ Defining dependencies
✤ Dependency Injection
✤ Test Doubles in Theory
✤ Test Doubles in Practice

3. What’s a dependency
✤ Unit Test Context
✤ A unit(s) of code that adds functionality to another unit of code
✤ Think system dependencies, but much smaller scale

4. Why mock them?
✤ Unit tests should cover a single unit of code in isolation
✤ A bug in a dependency makes your test a guessing game
✤ We only want to know that the code we’re testing works

5. Dependencies in the wild
class Auth
{
private $user;
public function __construct(User $user)
{
$this->user = $user;
}
public function authenticate()
{
$username = $this->user->getUserName();
$password = $this->user->getHash();
$this->checkLogin($username,$password);
}
}
Dependency Alert!

6. Don’t do this!
class Auth{ public function authenticate($username, $pass){ $user = new User($username, $pass);$username = $user->getUserName();$password = $user->getHash();$this->checkLogin($username,$password);}
User cannot be
mocked

7. Dependency Injection
✤ Helps make code testable
✤ Helps make code flexible
✤ Constructor/Accessor methods

8. MOAR Dependency Injection
✤ Dependencies become properties in the object in which they’re used
✤ Paramount for mocking in unit tests!

9. Mocking

10. Defining Test Doubles
✤ Stand in for actual objects (think Stunt Doubles)
✤ Can simulate functionality from those objects
✤ Can fulfill the requirements of a type hinted method
✤ Can be used to make sure a method on the mock is called

11. A few more points
✤ Can’t directly mock private or protected methods
✤ Only mock what you need to test
✤ In a pinch, Reflection API can help test private/protected

12. Theory
✤ Unit Test shouldn’t be dependent on external data source availability
✤ Unit Test vs. Integration Test
✤ “How do I know if my query is right?”
✤ You’re testing code, not network availability

13. Types of Test Doubles
✤ Mock
✤ Stub
✤ Dummy
✤ Spy

14. Mock
✤ Verifies that a method has been called correctly
✤ Doesn’t generate a response

15. Anatomy of a Mock
✤ Expectation
✤ Method
✤ Parameters (if applicable)

16. Mock Example
public function testSetUser()
{
$user = $this->getMock('User',array('setUserId'));
$user->expects($this->once())
->method('setUserId')
->with(1);
$post = new Post($user);
$post->retrieve(10);
$post->getUserInfo();
}

17. Explanation
✤ Supposes $user->setUserId(1) will be called in the test
✤ Fails if $user->setUserId(1) is not called

18. Mock Implementation
public function getUserInfo()
{
// assume $this->data is populated from
// the $post->retrieve($id) method
$userId = $this->data['user_id'];
$this->user->setUserId($userId);
return $this->user->retrieve();
}
This is an example of code that would pass the previous test,
it’s a fictional example...so I wouldn’t use the code :)

19. Test Stub
✤ Ensures a method is a called correctly
✤ Generates a “fake response”
✤ Response allows for different cases to be tested

20. Response

21. Stub Example
public function testGetUserInfo()
{
$userInfo = array(
'first_name' => 'Joe',
'last_name' => 'Strummer',
'id' => 1,
'email' => 'joe.strummer@gmail.com'
);
$user = $this->getMock('User', array('retrieve'));
$user->expects($this->once())
->method('retrieve')
->will($this->returnValue($userInfo));
...

22. Stub Example Cont’d
...
$post = new Post($user);
$post->retrieve(10);
$information = $post->getUserInfo();
$this->assertEquals('Joe',$information['first_name']);
$this->assertEquals('Strummer',$information['last_name']);
}
Here we’re asserting that retrieve is called correctly by validating
that we get back what we expect

23. Dummy
✤ It’s a place holder
✤ It has no expectations or behavior
✤ It satisfies a parameter list...

24. Dummy Example
<?php
class Comment
{
public function __construct($comment, User $user)
{
...
}
public function validateComment()
{
//doesn't rely on User at all
}
}

25. Dummy Example
public function testValidateComment()
{
$user = $this->getMock('User');
$commentText = "<script></script>";
$comment = new Comment($commentText,$user);
$this->assertFalse($comment->validateComment());
}
User fulfills the method signature, but doesn’t get used

26. Practical Examples!
✤ External Data Sources - don’t talk to em!
✤ APIs
✤ Database Responses

27. Stubbing PDO
✤ Constructor is not serializable, we must adapt!
✤ PDO::prepare - returns a PDO Statement (which we can stub)
✤ We can easily cover a variety of outcomes

28. Constructor
<?phpclass PDOTestHelper extends PDO{ public function __construct(){}}
Overridden constructor
allows us to mock!

29. Setup/TearDown
public function setUp()
{
$this->pdo = $this->getMock('PDOTestHelper');
$this->statement = $this->getMock('PDOStatement');
}
public function tearDown()
{
unset($pdo);
unset($statement);
}

30. Stubbing a prepared statement
$this->pdo->expects($this->once())
->method('prepare')
->with($this->stringContains('SELECT * from table'))
->will($this->returnValue($this->statement))
Prepare will return a PDOStatement when executed successfully, so in
order to stub the preparation and execution of the query, this is how we
need to start.

31. Stubbing the execute call
$this->statement->expects($this->once())
->method('execute')
->with($this->isType('array'))
->will($this->returnValue($this->statement));
Since we’re expecting this call to succeed, we need to return the
statement again. Once we get the statement back, we’ve successfully
simulated the preparation and execution of a query!

32. Stubbing Fetch!
$simData = array(
‘id‘ => 1,
‘firstName‘ => ‘Lloyd’,
‘lastName‘ => ‘Christmas’,
‘occupation‘ => ‘Dog Groomer’
);
$this->statement->expects($this->once())
->method('fetch')
->will($this->returnValue($simData));

33. Returning Data
✤ Data Fixtures
✤ Data Providers
✤ Data should resemble what you expect to get back

34. Mocking API Calls
✤ Wrap it up, not just for testing for your own sanity!
✤ Once it’s wrapped it can be mocked like anything else
✤ Spies!
✤ Don’t talk to the API

35. Spies
✤ Helpful in making sure your method was called
✤ Or called a certain number of times
✤ Not commonly used, but I’ve found good use in testing APIs

36. Practical API Testing
✤ Generally, mocks suffice!
✤ If the method is transforming data, stub it!
✤ Spies are good to track multiple calls in same method

37. API Example
public function testGetTweets()
{
//mock example
$request = $this->getMock('Request',array('get'));
$request->expects($this->once())
->method('get')
->with('statuses');
$twitter = new Twitter($request);
$twitter->getTweets();
}

38. Spy Example
public function testComplicatedMethod()
{
//spy example
$request = $this->getMock('Request',array('get'));
$request->expects($this->exactly(3))
->method('get');
$twitter = new Twitter($request);
$twitter->complicatedMethod();
}

39. Helpful Tidbits - With()
✤ isType(String $type) - check by type
✤ stringContains($value) - string parameter
✤ contains($value) - array parameter
✤ hasArrayKey($key)
✤ greaterThan($value)
✤ isInstanceOf($className)
✤ matchesRegularExpression($pattern)
✤ equalTo($value)

40. Summary
✤ Injected Dependencies = Increased Testability
✤ Mock/Stub/Dummy
✤ Don’t do more than you need to!
✤ Practice makes perfect

41. Victory!
Mocking effectively leads to better tests and better tests lead to
better applications!

42. Thank you!
✤ Freenode: mfrost503
✤ Joind.in: http://joind.in/8693