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Creating Partial Mocks

Partial mocks are useful when you only need to mock several methods of an object leaving the remainder free to respond to calls normally (i.e. as implemented). Mockery implements three distinct strategies for creating partials. Each has specific advantages and disadvantages so which strategy you use will depend on your own preferences and the source code in need of mocking.

  1. Traditional Partial Mock
  2. Passive Partial Mock
  3. Proxied Partial Mock

Traditional Partial Mock

A traditional partial mock defined ahead of time which methods of a class are to be mocked and which are to left unmocked (i.e. callable as normal). The syntax for creating traditional mocks is:

$mock = \Mockery::mock('MyClass[foo,bar]');

In the above example, the foo() and bar() methods of MyClass will be mocked but no other MyClass methods are touched. You will need to define expectations for the foo() and bar() methods to dictate their mocked behaviour.

Don't forget that you can pass in constructor arguments since unmocked methods may rely on those!

$mock = \Mockery::mock("MyNamespace\MyClass[foo]", array($arg1, $arg2));

Passive Partial Mock

A passive partial mock is more of a default state of being.

$mock = \Mockery::mock('MyClass')->makePartial();

In a passive partial, we assume that all methods will simply defer to the parent class (MyClass) original methods unless a method call matches a known expectation. If you have no matching expectation for a specific method call, that call is deferred to the class being mocked. Since the division between mocked and unmocked calls depends entirely on the expectations you define, there is no need to define which methods to mock in advance. The makePartial() method is identical to the original shouldDeferMissing() method which first introduced this Partial Mock type.

Proxied Partial Mock

A proxied partial mock is a partial of last resort. You may encounter a class which is simply not capable of being mocked because it has been marked as final. Similarly, you may find a class with methods marked as final. In such a scenario, we cannot simply extend the class and override methods to mock - we need to get creative.

$mock = \Mockery::mock(new MyClass);

Yes, the new mock is a Proxy. It intercepts calls and reroutes them to the proxied object (which you construct and pass in) for methods which are not subject to any expectations. Indirectly, this allows you to mock methods marked final since the Proxy is not subject to those limitations. The tradeoff should be obvious - a proxied partial will fail any typehint checks for the class being mocked since it cannot extend that class.

Special Internal Cases

All mock objects, with the exception of Proxied Partials, allow you to make any expectation call the underlying real class method using the passthru() expectation call. This will return values from the real call and bypass any mocked return queue (which can simply be omitted obviously).

There is a fourth kind of partial mock reserved for internal use. This is automatically generated when you attempt to mock a class containing methods marked final. Since we cannot override such methods, they are simply left unmocked. Typically, you don't need to worry about this but if you really really must mock a final method, the only possible means is through a Proxied Partial Mock. SplFileInfo, for example, is a common class subject to this form of automatic internal partial since it contains public final methods used internally.

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