Mock objects

Sometimes when writing tests you need to test something that depends on an object being in a certain state.

Say for example you're testing a model - you want to make sure that the model is running the correct query, but you don't want it to run on a real database server. You can create a mock database connection which responds in the way the model expects, but doesn't actually connect to a physical database.

PHPUnit has a built in mock object creator which can generate mocks for classes (inc. abstract ones) on the fly.
It creates a class that extends the one you want to mock. You can also tell PHPUnit to override certain functions to return set values / assert that they're called in a specific way.

Creating an instance of a mock class

You create mocks from within testcases using the getMock() function, which is defined in PHPUnit_Framework_TestCase like so:

    getMock($originalClassName, $methods = array(), array $arguments = array(), $mockClassName = '', $callOriginalConstructor = TRUE, $callOriginalClone = TRUE, $callAutoload = TRUE)
The name of the class that you want to mock
The methods of $originalClassName that you want to mock.
You need to tell PHPUnit in advance because PHP doesn't allow you to extend an object once it's been initialised.
An array of arguments to pass to the mock's constructor
Allows you to specify the name that will be given to the mock
Should the mock call its parent's constructor automatically?
Should the mock call its parent's clone method?

Most of the time you'll only need to use the first two parameters, i.e.:

$mock = $this->getMock('ORM');

$mock now contains a mock of ORM and can be handled as though it were a vanilla instance of ORM

$mock = $this->getMock('ORM', array('check'));

$mock now contains a mock of ORM, but this time we're also mocking the check() method.

Mocking methods

Assuming we've created a mock object like so:

$mock = $this->getMock('ORM', array('check'));

We now need to tell PHPUnit how to mock the check function when its called.

How many times should it be called?

You start off by telling PHPUnit how many times the method should be called by calling expects() on the mock object:


expects() takes one argument, an invoker matcher which you can create using factory methods defined in PHPUnit_Framework_TestCase:

Possible invoker matchers:

Returns a matcher that allows the method to be called any number of times
Returns a matcher that asserts that the method is never called
Returns a matcher that asserts that the method is only called once
Returns a matcher that asserts that the method is called at least once
Returns a matcher that asserts that the method is called at least $count times
Returns a matcher that matches when the method it is evaluated for is invoked at the given $index.

In our example we want check() to be called once on our mock object, so if we update it accordingly:

$mock = $this->getMock('ORM', array('check'));


What is the method we're mocking?

Although we told PHPUnit what methods we want to mock, we haven't actually told it what method these rules we're specifiying apply to.
You do this by calling method() on the returned from expects():


As you can probably guess, method() takes one parameter, the name of the method you're mocking.
There's nothing very fancy about this function.

$mock = $this->GetMock('ORM', array('check'));


What parameters should our mock method expect?

There are two ways to do this, either

  • Tell the method to accept any parameters
  • Tell the method to accept a specific set of parameters

The former can be achieved by calling withAnyParameters() on the object returned from method()


To only allow specific parameters you can use the with() method which accepts any number of parameters.
The order in which you define the parameters is the order that it expects them to be in when called.

    ->with($param1, $param2);

Calling with() without any parameters will force the mock method to accept no parameters.

PHPUnit has a fairly complex way of comparing parameters passed to the mock method with the expected values, which can be summarised like so -

  • If the values are identical, they are equal
  • If the values are of different types they are not equal
  • If the values are numbers they they are considered equal if their difference is equal to zero (this level of accuracy can be changed)
  • If the values are objects then they are converted to arrays and are compared as arrays
  • If the values are arrays then any sub-arrays deeper than x levels (default 10) are ignored in the comparision
  • If the values are arrays and one contains more than elements that the other (at any depth up to the max depth), then they are not equal

More advanced parameter comparisions

Sometimes you need to be more specific about how PHPUnit should compare parameters, i.e. if you want to make sure that one of the parameters is an instance of an object, yet isn't necessarily identical to a particular instance.

In PHPUnit, the logic for validating objects and datatypes has been refactored into "constraint objects". If you look in any of the assertX() methods you can see that they are nothing more than wrappers for associating constraint objects with tests.

If a parameter passed to with() is not an instance of a constraint object (one which extends PHPUnit_Framework_Constraint) then PHPUnit creates a new IsEqual comparision object for it.

i.e., the following methods produce the same result:

->with('foo', 1);

->with($this->equalTo('foo'), $this->equalTo(1));

Here are some of the wrappers PHPUnit provides for creating constraint objects:

Asserts that the parameter will have an element with index $key
$this->attribute(PHPUnit_Framework_Constraint $constraint, $attributeName)
Asserts that object attribute $attributeName of the parameter will satisfy $constraint, where constraint is an instance of a constraint (i.e. $this->equalTo())
Accepts no parameters, asserts that the parameter is a path to a valid file (i.e. file_exists() === TRUE)
Asserts that the parameter is greater than $value
Returns TRUE regardless of what the parameter is
$this->equalTo($value, $delta = 0, $canonicalizeEOL = FALSE, $ignoreCase = False)
Asserts that the parameter is equal to $value (same as not passing a constraint object to with())
$delta is the degree of accuracy to use when comparing numbers. i.e. 0 means numbers need to be identical, 1 means numbers can be within a distance of one from each other
If $canonicalizeEOL is TRUE then all newlines in string values will be converted to \n before comparision
If $ignoreCase is TRUE then both strings will be converted to lowercase before comparision
Asserts that the parameter is identical to $value
Asserts that the parameter is of type $type, where $type is a string representation of the core PHP data types
Asserts that the parameter is an instance of $className
Asserts that the parameter is less than $value
Asserts that the paramater (which is assumed to be an object) has an attribute $attribute
Asserts that the parameter matches the PCRE pattern $pattern (using preg_match())
$this->stringContains($string, $ignoreCase = FALSE)
Asserts that the parameter contains the string $string. If $ignoreCase is TRUE then a case insensitive comparision is done
Asserts that the parameter ends with $suffix (assumes parameter is a string)
Asserts that the parameter starts with $prefix (assumes parameter is a string)
Asserts that the parameter contains at least one value that is identical to $value (assumes parameter is array or SplObjectStorage)
$this->containsOnly($type, $isNativeType = TRUE)
Asserts that the parameter only contains items of type $type. $isNativeType should be set to TRUE when $type refers to a built in PHP data type (i.e. int, string etc.) (assumes parameter is array)

There are more constraint objects than listed here, look in PHPUnit_Framework_Assert and PHPUnit/Framework/Constraint if you need more constraints.

If we continue our example, we have the following:


So far PHPUnit knows that we want the check() method to be called once, with no parameters. Now we just need to get it to return something...

What should the method return?

This is the final stage of mocking a method.

By default PHPUnit can return either

  • A fixed value
  • One of the parameters that were passed to it
  • The return value of a specified callback

Specifying a return value is easy, just call will() on the object returned by either method() or with().

The function is defined like so:

public function will(PHPUnit_Framework_MockObject_Stub $stub)

PHPUnit provides some MockObject stubs out of the box, you can access them via (when called from a testcase):

Returns $value when the mocked method is called
Returns the $argumentIndexth argument that was passed to the mocked method
Returns the value of the callback, useful for more complicated mocking.
$callback should a valid callback (i.e. is_callable($callback) === TRUE). PHPUnit will pass the callback all of the parameters that the mocked method was passed, in the same order / argument index (i.e. the callback is invoked by call_user_func_array()).
You can usually create the callback in your testcase, as long as doesn't begin with "test"

Obviously if you really want to you can create your own MockObject stub, but these three should cover most situations.

Updating our example gives:


And we're done!

If you now call $mock->check() the value TRUE should be returned.

If you don't call a mocked method and PHPUnit expects it to be called then the test the mock was generated for will fail.