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Filename : big_parent_class.rst
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Big Parent Class
================

In some application code, especially older legacy code, we can come across some
classes that extend a "big parent class" - a parent class that knows and does
too much:

.. code-block:: php

    class BigParentClass
    {
        public function doesEverything()
        {
            // sets up database connections
            // writes to log files
        }
    }

    class ChildClass extends BigParentClass
    {
        public function doesOneThing()
        {
            // but calls on BigParentClass methods
            $result = $this->doesEverything();
            // does something with $result
            return $result;
        }
    }

We want to test our ``ChildClass`` and its ``doesOneThing`` method, but the
problem is that it calls on ``BigParentClass::doesEverything()``. One way to
handle this would be to mock out **all** of the dependencies ``BigParentClass``
has and needs, and then finally actually test our ``doesOneThing`` method. It's
an awful lot of work to do that.

What we can do, is to do something... unconventional. We can create a runtime
partial test double of the ``ChildClass`` itself and mock only the parent's
``doesEverything()`` method:

.. code-block:: php

    $childClass = \Mockery::mock('ChildClass')->makePartial();
    $childClass->shouldReceive('doesEverything')
        ->andReturn('some result from parent');

    $childClass->doesOneThing(); // string("some result from parent");

With this approach we mock out only the ``doesEverything()`` method, and all the
unmocked methods are called on the actual ``ChildClass`` instance.